ClearSpringRanch SolidsHandling&DisposalFacility Masterplan

December19,2003

Table of Contents

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Executive Summary ...... ES-1 Overview...... ES-1 Existing Facilities ...... ES-1 Population, Flow, and Loading Values and Projections ...... ES-1 Capacity Evaluation...... ES-2 Recommended Improvements to the Solids Handling, Treatment, and Disposal System...... ES-2 Grease Handling Improvements ...... ES-3 Raw Sludge Thickening/Centrate Treatment ...... ES-3 Digestion Modifications...... ES-5 FSB Expansion...... ES-5 Improved and Modified DLD System...... ES-5 Water Management...... ES-6 Implementation of the Preferred System...... ES-6

Chapter 1. Background...... 1-1 Overview...... 1-1 Purpose of Study...... 1-1 Study Scope...... 1-1 Existing System ...... 1-2 Blended Sludge Pump Station...... 1-2 Sludge Transmission Main...... 1-3 Anaerobic Digesters ...... 1-3 Facultative Sludge Basins...... 1-3 Dedicated Land Disposal...... 1-3 Site Water Management ...... 1-3 Planning Organization ...... 1-4

Chapter 2. Solids Projections ...... 2-1 Introduction...... 2-1 Projections ...... 2-1 Projected Population ...... 2-1 Projected Raw Sludge Production ...... 2-4 Projected Grit and Screenings...... 2-8 Projected Scum...... 2-9 Summary...... 2-10

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Table of Contents (continued)

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Chapter 3. Evaluation of the Capacity of the Existing System and Operations ...... 3-1 Introduction...... 3-1 Description of Major Process Units ...... 3-1 Blended Sludge Pump Station...... 3-1 Sludge Main...... 3-1 Anaerobic Digesters ...... 3-1 Facultative Sludge Basins (FSBs) ...... 3-2 Dedicated Land Disposal (DLD) System...... 3-2 Supernatant Handling System ...... 3-3 Process Design Criteria and Performance ...... 3-3 Projected Capacity ...... 3-6 Blended Sludge Pump Station...... 3-6 Anaerobic Digester...... 3-7 Facultative Sludge Basins...... 3-9 Dedicated Land Disposal (DLD) ...... 3-10 Capacity Summary...... 3-11

Chapter 4. Existing and Potential Future Regulatory Requirements ...... 4-1 Overview...... 4-1 Air Quality Requirements...... 4-1 Endangered Species Act ...... 4-4 State Sensitive Species ...... 4-7 Biosolids Disposal and Utilization Issues...... 4-10 Federal Sludge Regulation Requirements (40 CFR, Part 503) and Current Sludge (Biosolids) Characteristics...... 4-10 Metal Concentrations of Biosolids ...... 4-13 Site Restrictions/Management Practices for Class A or B Biosolids (503.14)...... 4-14 Class B Additional Site Restrictions for Cropland...... 4-14 Monitoring Requirements for Sludge Application...... 4-15 Record Keeping and Reporting ...... 4-15 Other Considerations for Class A or B Biosolids Application ...... 4-15 Future Regulatory Considerations...... 4-16 State, Regional, and Local Regulations...... 4-16 State Regulations...... 4-16 Regional Regulations ...... 4-17

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Table of Contents (continued)

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Chapter 5. Options for Beneficial Use of Biosolids ...... 5-1 Introduction...... 5-1 Beneficial Use – Class B ...... 5-1 On-Site Land Application – Slurry...... 5-2 Off-Site Agricultural Land Application (Primarily Dewatered Cake) ...... 5-2 Off-Site Land Application – Air Dried...... 5-3 Off-Site Landfill Cover or Land or Mine Reclamation ...... 5-4 Beneficial Use – Class A ...... 5-4 Heat Dried Product ...... 5-5 Composted Product...... 5-6 Land Application Using Cake Product...... 5-7 Land Application Using Air Dried Product...... 5-8 Landfill Cover or Land Reclamation – Cake Product ...... 5-8 Landfill Cover or Land Reclamation – Air-Dried...... 5-9 Biosolids Beneficial Use Options In Colorado ...... 5-9 Local Beneficial Use Study ...... 5-9 Local Examples of Beneficial Biosolids Application...... 5-10 Biosolids Compost Production and Use ...... 5-11 Marketability of Biosolids Products ...... 5-11 Public Acceptance and Concerns ...... 5-12

Chapter 6. Process, Treatment, and Disposal Options ...... 6-1 Overview...... 6-1 Pumping and Thickening Raw Sludge...... 6-1 Pumping Sludge to the SHDF ...... 6-1 Other Long Sludge Pipeline Situations...... 6-4 Sludge Velocity and Gas Production in the Sludge Main ...... 6-5 Pumping Thinner Sludge to the SHDF...... 6-6 Modified Thickening at Las Vegas Street WWTP ...... 6-7 Sludge Thickening at the SHDF...... 6-7 Thickening Centrate Handling/Processing...... 6-9 Processing and Final Use/Disposal of Centrate or Excess FSB Supernatant ...... 6-10 Sludge Thickening System at the SHDF ...... 6-11 Recuperative Thickening at the Digestion Facilities...... 6-11 Followup Needs...... 6-12 Anaerobic Digestion...... 6-13 Struvite Production and Control ...... 6-13 Debris Processing and Removal ...... 6-16 Disintegration Using Ultrasound Technology...... 6-17 Thermal Hydrolysis...... 6-18 Pre-Pasteurization ...... 6-19 Digestion Process Evaluation ...... 6-21

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Table of Contents (continued)

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Current Anaerobic Digestion System ...... 6-23 Acid Digestion Within the Sludge Main...... 6-23 Acid/Gas Phased Digestion at the SHDF...... 6-24 Thermophilic Digestion...... 6-28 Temperature Phased Digestion...... 6-30 Achieving Class A Within Thermophilic Digestion Systems ...... 6-30 Digestion Capacity at the SHDF With Thickening ...... 6-31 Class B Digestion Alternatives at the SHDF...... 6-32 Class A Digestion Alternatives at the SHDF...... 6-34 Iron Chloride Addition ...... 6-37 Post-Digestion Storage...... 6-37 Digester Improvements ...... 6-37 Digester Mixing...... 6-39 FSB Options/Improvements...... 6-41 Additional FSBs...... 6-41 FSB Feeding/Loading of FSBs...... 6-42 Solids Destruction Within FSBs ...... 6-43 FSB Inventory and Management...... 6-44 Dredging FSBs ...... 6-44 Long-Term FSB Storage for Class A Biosolids...... 6-45 Additional Solids Testing...... 6-46 DLD Options/Improvements...... 6-46 Options to Control Groundwater Beneath DLDs ...... 6-46 DLD Improvements and Equipment Modifications...... 6-47 Current and Future DLD Capacity ...... 6-48 Site Monitoring and Testing...... 6-49 Dewatering...... 6-50 Belt Filter Presses...... 6-51 Centrifuges...... 6-54 Fournier Rotary Press...... 6-57 FKC Screw Press...... 6-59 Dewatering/Drying Processes ...... 6-61 Centridry™ ...... 6-61 Vacuum/High Temperature Pressure Filters ...... 6-62 Filtrate/Centrate Processing and Recycle ...... 6-63 Dewatering Summary ...... 6-64 Heat Drying ...... 6-64 Vendor-Provided Systems ...... 6-65 Process Operations Considerations ...... 6-68 Development of Drying Option...... 6-69 Fuel Source (Digester Gas)...... 6-69

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Table of Contents (continued)

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Air Drying of Biosolids...... 6-70 Air Drying and Associated Processes ...... 6-70 Air-Drying Operations in Colorado...... 6-70 Larger-Scale Air Drying Facilities...... 6-71 Approach for SHDF Air Drying ...... 6-72 Air-Drying Slurry...... 6-72 Air-Drying Dewatered Cake...... 6-73 Recirculating Fluidized Bed Boiler (RFBB) ...... 6-73 Off-Site Beneficial Use and Disposal Modes ...... 6-74 Land Application of Class A Material...... 6-74 Emergency Back-Up DLD Disposal Options...... 6-75 Composting...... 6-76 Initial Disposal/Beneficial Use Process Screening ...... 6-76 Alternative Selection...... 6-78

Chapter 7. Alternative Evaluation ...... 7-1 Overview...... 7-1 Alternative 1 – Modified or Improved FSB/DLD System...... 7-1 Thickening Prior to Digestion ...... 7-1 Digestion ...... 7-3 Additional FSBs...... 7-4 Improved and Modified DLD System...... 7-4 Dewatering...... 7-4 Alternative 2 - Class A (Heat Dry) and Beneficial Use ...... 7-5 Thickening Prior to Digestion ...... 7-5 Digestion ...... 7-5 Reduced FSB Operation ...... 7-5 Reduced DLD Operation...... 7-5 Dewatering...... 7-5 Heat Drying System...... 7-7 Alternative 3 - Class A (Digestion) and Beneficial Use (Dewater and Air-Dry FSB-Harvested Biosolids)...... 7-7 Thickening Prior to Digestion ...... 7-7 Digestion ...... 7-9 Additional FSBs...... 7-9 Reduced DLD Operation...... 7-9 Dewatering...... 7-9 Air Drying Operation...... 7-10

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Table of Contents (continued)

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Alternative 4 - Class A (Digestion) and Beneficial Use (Dewater and Air-Dry Portion of Digested Slurry)...... 7-10 Thickening Prior to Digestion ...... 7-10 Digestion ...... 7-10 FSBs ...... 7-12 DLD Operation...... 7-12 Dewatering...... 7-12 Air Drying Operation...... 7-12 Alternative 5 – Sludge Cake to Recirculating Fluidized Bed Boiler ...... 7-12 Dewatering...... 7-13 RFBB ...... 7-15 Reduced Digestion...... 7-15 Reduced FSB Operation ...... 7-15 Reduced DLD Operation...... 7-15 Economic and Noneconomic Comparison of Alternatives...... 7-15 Overall Comparisons and Conclusions ...... 7-19

Chapter 8. Use of Digester Gas for Energy Production...... 8-1 Overview...... 8-1 Biogas Utilization...... 8-1 Available Digester Gas...... 8-2 Cogeneration ...... 8-2 General ...... 8-2 Dual Fuel System ...... 8-3 Internal Combustion Engine...... 8-3 Maintenance...... 8-3 Cogeneration Alternative...... 8-3 Alternative Generation Technologies...... 8-4 Induction Generators ...... 8-4 Microturbines...... 8-5 Fuel Cells...... 8-5 Other Uses for Gas ...... 8-7 Operation of Process Equipment...... 8-7 Air Conditioning ...... 8-7 Conversion of Biogas to Methanol ...... 8-8 Energy Source for Nearby Industries ...... 8-9 Evaluation of Biogas Utilization Technologies...... 8-9 Economic Evaluation...... 8-10 Cogeneration Economics...... 8-10 Economics of Exchanging Biogas for Power Plant Steam...... 8-11 Microturbine Economics...... 8-12

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Table of Contents (continued)

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Overall Comparison ...... 8-13 Recommendations ...... 8-14

Chapter 9. Environmental Evaluation ...... 9-1 Objective...... 9-1 Groundwater Issues...... 9-1 General Description of SHDF Water Management...... 9-1 Water Study Evaluation...... 9-2 Groundwater Level Monitoring...... 9-3 Groundwater and Process Quality Monitoring ...... 9-3 Air Emission and Odor Control Evaluations...... 9-4 Odor Control...... 9-6 Recommendations ...... 9-7 Water Management Plan...... 9-7 Other Water Treatment Options...... 9-7 Air Emissions ...... 9-8

Chapter 10. Siting and Landscape Architecture Planning...... 10-1 Introduction...... 10-1 History 10-1 Future Considerations...... 10-1 Locations for Improvements ...... 10-3 Raw Sludge Thickening...... 10-3 Raw Sludge Dewatering ...... 10-3 Digested or Harvested Sludge Dewatering ...... 10-5 FSB Expansion...... 10-7 DLD Expansion...... 10-7 Heat Drying ...... 10-7 Air Drying ...... 10-8 Appearance of New Buildings ...... 10-8 Basic Criteria...... 10-8 Lower Fountain Water Reclamation Facility ...... 10-9 Proposed Location...... 10-9 Irrigation and Landscaping...... 10-9 Water Availability...... 10-9 Regulatory and Health Issues...... 10-11 Site Land Use Planning ...... 10-11

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Table of Contents (continued)

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Chapter 11. Recommended Alternative for Future Facility Improvements...... 11-1 Introduction...... 11-1 Recommended Existing System Improvements ...... 11-4 Grease Handling Improvements ...... 11-4 Raw Sludge Thickening/Centrate Treatment ...... 11-4 Digestion Modifications...... 11-6 FSB Expansion...... 11-6 Improved and Modified DLD System...... 11-6 Water Management...... 11-7 Sludge Screening at Las Vegas Street WWTP BSPS...... 11-8 Timing of Improvements ...... 11-8 Refined Capital Costs...... 11-8 Annual O&M Costs...... 11-12

Chapter 12. Capital Improvement Plan/Financial Plan ...... 12-1 Objective...... 12-1 Capital Improvements Plan...... 12-1 Detailed Project Information Sheets...... 12-1

Chapter 13. References...... 13-1

TABLES

Table ES-1. Existing and Projected Populations and Flows ...... ES-2

Table 2-1. Comparison of Recent Population Projections For The Colorado Springs Area and El Paso County...... 2-2 Table 2-2. Historic and Projected Flows to the Las Vegas Street WWTF ...... 2-3 Table 2-3. City of Colorado Springs Historical Sludge Production...... 2-5 Table 2-4. City of Colorado Springs Annual Average Raw Sludge Projections...... 2-5 Table 2-5. El Paso County Annual Average Raw Sludge Projections...... 2-6 Table 2-6. Solids Quantities Comparison to Similar Facilities ...... 2-8 Table 2-7. Estimated Future Screenings and Grit Quantities (Based on Colorado Springs Population) ...... 2-9 Table 2-8. Estimated Future Screenings and Grit Quantities (Based on El Paso County Projected Population) ...... 2-9 Table 2-9. Estimated Scum Quantities (Based on Colorado Springs Population) ...... 2-10 Table 2-10. Estimated Scum Quantities (Based on El Paso County Projected Population)...... 2-10

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Table of Contents (continued)

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Table 3-1. Process Design Criteria and System Performance for 2001 and 2002...... 3-3 Table 3-2. Effects of Higher Solids Concentrations on Hydraulic Capacity in the Anaerobic Digesters...... 3-4 Table 3-3. Mass Balance Comparison ...... 3-4 Table 3-4. VSR Reduction Summary...... 3-11

Table 4-1. Permitted Air Emissions ...... 4-1 Table 4-2. Significant Net Emissions Increase ...... 4-2 Table 4-3. Colorado Endangered Species...... 4-6 Table 4-4. El Paso County Endangered Species...... 4-7 Table 4-5. El Paso County – State Sensitive Species ...... 4-8 Table 4-6. Summary of the Six Process Alternatives for Meeting Class A Pathogen Requirements ...... 4-10 Table 4-7. Pathogen Requirements for All Class A Alternatives ...... 4-11 Table 4-8. Processes to Further Reduce Pathogens (PFRPs) Listed in Appendix B of 40 CFR Part 503...... 4-11 Table 4-9. Summary of the Three Alternatives for Meeting Class B Pathogen Requirements...... 4-12 Table 4-10. Processes to Significantly Reduce Pathogens (PSRPs) Listed in Appendix B of 40 CFR Part 503...... 4-12 Table 4-11. Options for Meeting Vector Attraction Reduction...... 4-13 Table 4-12. Comparison of Average Monthly Metals Concentrations to Part 503 Limits...... 4-14 Table 4-13. Monitoring Requirements for Biosolids Application...... 4-15

Table 6-1. Sludge Main and Solids Characteristics...... 6-2 Table 6-2. Long Raw Sludge Pipelines and Operating Conditions...... 6-5 Table 6-3. Alternative Pumping Conditions in the 14-inch Sludge Main...... 6-7 Table 6-4. Raw Sludge Thickening at the SHDF (assuming 700,000 gal/day sludge flowrate)...... 6-8 Table 6-5. Estimated Excess Water Characteristics...... 6-9 Table 6-6. Excess Water Handling Options at the Clear Spring Ranch ...... 6-10 Table 6-7. Possible Precipitants for Conditions Within Anaerobic Digesters...... 6-14 Table 6-8. Advanced Anaerobic Digestion Process Information...... 6-25 Table 6-9. Future Digester Capacity at the SHDF...... 6-32 Table 6-10. Estimate of VSR for Digestion Alternatives...... 6-34 Table 6-11. Projected FSB Loading Rate...... 6-42 Table 6-12. Additional FSBs Required for Current System Operation and Class A “2-year Pure Storage” Operation ...... 6-46 Table 6-13. Projected DLD Loading Based on Additional Acreage ...... 6-49 Table 6-14. Summary of Advantages/Disadvantages for Belt Presses ...... 6-54 Table 6-15. Summary of Operational Issues for Belt Press ...... 6-54 Table 6-16. Expected Performance of Belt Presses...... 6-54

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Table 6-17. Summary of Advantages/Disadvantages for Centrifuges...... 6-56 Table 6-18. Summary of Operational Issues for Centrifuges ...... 6-56 Table 6-19. Expected Performance of Centrifuges...... 6-57 Table 6-20. Summary of Advantages/Disadvantages for Fournier Rotary Press...... 6-58 Table 6-21. Summary of Operational Issues for Fournier Rotary Press...... 6-59 Table 6-22. Summary of Advantages/Disadvantages for FKC Screw Press ...... 6-60 Table 6-23. Summary of Operational Issues for FKC Screw Press...... 6-61 Table 6-24. SHDF Digester Gas Production (Cubic Feet per Day)...... 6-69 Table 6-25. Landfill Summary ...... 6-76 Table 6-26. Initial Assessment of Sludge Disposal and Beneficial Use Options...... 6-77 Table 6-27. Selected Disposal/Beneficial Use Alternatives for Evaluation...... 6-78

Table 7-1. Solids Alternative Cost and Economic Comparison...... 7-16 Table 7-2. Non-Economic Comparison...... 7-18 Table 7-3. Alternative Net Present Value Comparison ...... 7-19

Table 8-1. Digester Gas Production and Usage (scf)...... 8-2 Table 8-2. Gas Utilization Technology Factors...... 8-9 Table 8-3. Economic Comparison...... 8-13

Table 9-1. Water Quality Data for Salinity and Nitrate...... 9-4

Table 10-1. Estimated Excess Water Characteristics...... 10-11

Table 11-1. Alternative 1 Estimated Total Project Cost...... 11-9 Table 11-2. Projected Annual O&M Costs (dollars/yr) ...... 11-12

Table 12-1. Expected Cost Disbursement...... 12-3

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FIGURES

Figure ES-1. Modified or Improved FSB/DLD System...... ES-4 Figure ES-2. Expected Cost Disbursement...... ES-7 Figure ES-3. Program Capital Expenditures ...... ES-8

Figure 2-1. Comparison of Historic Population and Projections For The Colorado Springs Area and El Paso County...... 2-3 Figure 2-2. Historical and Projected Flows for the Colorado Springs Area and El Paso County...... 2-4 Figure 2-3. Historic and Projected Annual Average Sludge Values at the Las Vegas Street WWTF BSPS and Influent to the Digesters at the SHDF...... 2-6 Figure 2-4. Historic and Projected Annual Average Pounds per Million Gallons at the Las Vegas Street WSWTF BSPS and Influent to the Digesters at the SHDF ...... 2-7

Figure 3-1. Projected Annual Average Solids Loading Rate to the SHDF...... 3-6 Figure 3-2. Blended Sludge Pump Station – Capacity vs. Projected Flows (3.1% Solids)...... 3-7 Figure 3-3. Anaerobic Digesters – Capacity vs. Projected Solids Loading Rate (Peak Week)...... 3-8 Figure 3-4. Anaerobic Digesters – Hydraulic Capacity vs. Projected Flows (Peak Week)...... 3-9 Figure 3-5. Facultative Sludge Basins – Capacity vs. Projected Loading ...... 3-10 Figure 3-6. Dedicated Land Disposal – Capacity vs. Projected Loading (based on 194 acres)...... 3-11

Figure 6-1. Recuperative Thickening...... 6-12 Figure 6-2. EPA Alternative 1 Time/Temp Equation Comparisons ...... 6-19 Figure 6-3. Process Schematic Diagrams – Advanced and Phased/Staged Digestion...... 6-22 Figure 6-4. Class B Digestion Alternatives ...... 6-33 Figure 6-5. Class A Digestion Alternatives...... 6-35

Figure 7-1. Alternative 1 – Modified or Improved FSB/DLD System...... 7-2 Figure 7-2. Alternative 2 – Class A (Heat Dry) and Beneficial Use...... 7-6 Figure 7-3. Alternative 3 – Class A (Digestion) and Beneficial Use ...... 7-8 Figure 7-4. Alternative 4 – Class A (Digestion) and Beneficial Use (Portion) ...... 7-11 Figure 7-5. Alternative 5 – Sludge Cake to RFBB...... 7-14

Figure 10-1. Existing SHDF Site Plan...... 10-2 Figure 10-2. Proposed Improvements...... 10-4 Figure 10-3. Potential Raw Sludge Dewatering Location For RFBB Alternative...... 10-6 Figure 10-4. “Figure 3” From MWH, Memorandum RE: ...... Lower Fountain Regional Water Reclamation Facility Siting Study, August 18, 2003 ...... 10-10

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Figure 11-1. Alternative 1 – Modified or Improved FSB/DLD System...... 11-2 Figure 11-2. Alternative 1 Recommended Improvements ...... 11-3

Figure 12-1. Proposed Implementation Schedule...... 12-2 Figure 12-2. Program Capital Expenditures ...... 12-4

APPENDICES

Appendix A: Cost/Economic Criteria and Assumptions for the Solids Evaluation of the Clear Spring Ranch SHDF Masterplan Appendix B: Explanation of Comparison Ratings in Table 7-1 Appendix C: Detailed Cost Estimates

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Executive Summary

Overview The 2003 Clear Spring Ranch Solids Handling & Disposal Facility (SHDF) Masterplan was developed for Colorado Springs Utilities by Brown and Caldwell in cooperation with Colorado Springs Utilities’ operations, environmental, engineering and planning staff. The planning period covers 22 years, from 2003 through 2025.

Existing Facilities The facilities at the SHDF currently consist of eight anaerobic digesters, a digester equipment building, an energy recovery building, dedicated land disposal (DLD) areas, a pumping/ maintenance building, nine facultative sludge basins (FSBs), and two supernatant lagoons. An expansion of these facilities was completed in early 2000. The expansion project included four new digesters and three new FSBs as the major improvements. The SHDF has had a history of excellent performance. Since start-up, the facility has consistently met treatment objectives and has been recognized as a well managed and efficient operation.

The SHDF is located about 17 miles southwest of downtown Colorado Springs. The facility became operational in 1984 and serves as a disposal site for the following materials.

§ Fly ash from the R.D. Nixon Power Plant located north of the SHDF on the Clear Spring Ranch site and the Drake Power Plant near downtown. § Brine from the Zero Discharge Treatment Facility located on the Clear Spring Ranch site, which treats blowdown from the power plants and recycles it back to the cooling towers. § Sludge, screenings, and grit from the Las Vegas Street Wastewater Treatment Facility (WWTF).

Population, Flow, and Loading Values and Projections This Masterplan relies upon projections of population and wastewater flows and loadings to determine future solids handling, treatment, and disposal needs. Population projections for this Masterplan were obtained for local and regional levels of treatment. The City of Colorado Springs’ historical population values (1990-2001) were provided by the State Demographers Office (April 2003). Colorado Springs projected population (2002-2025) are Colorado Springs Utilities’ internal projections, which were derived from the El Paso County Global Insight (September 2002) forecasts. Colorado Springs projections include Manitou and Peterson Field. The El Paso County historical and projected population was obtained from Global Insight (September 2002). Entities included in the El Paso County forecasts include Colorado Springs, Calhan, Fountain, Green Mountain Falls, Manitou Springs, Monument, Palmer Lake, and Unincorporated El Paso County. For the purposes of projecting wastewater flows and sludge quantities, 120 gallons per person per

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day and 0.23 pounds per person per day, respectively was applied to the residential population. The total population, flows, and loading in 2000 and 2025 for the existing service area and for the entire El Paso County are outlined in Table ES-1.

Table ES-1. Existing and Projected Populations and Flows 2000 2025 Projected Avg Projected Avg Avg Flow at Las Avg Raw Sludge Flow at Las Vegas Sludge at Vegas Street at WWTF Projected Street WWTF WWTF (ppd – Service Area Population WWTF (mgd) (ppd-dry weight) Population (mgd)* dry weight) Colorado Springs Area (Existing 360,890 45.5 76,303 505,691 60.8 118,212 Service Area) El Paso County 519,716 -- -- 741,500 89.2 173,335 * Based on hypothetical case without Northern Water Reclamation Facility or any other regional plants.

Capacity Evaluation Since 2001, the FSBs have been operated at the design capacity established in the Basis of Design Memorandum, dated May 8, 1997 and are the limiting process.

The anaerobic digesters are the second limiting process at the SHDF. The capacity analysis revealed the digesters should be able to treat projected solids loads until approximately 2020 based on the Colorado Springs projections (existing service area) and through 2005 based on the entire El Paso County projections. However, if the solids loading rate is increased to 0.1 lb VSS/ft3/day as recommended by process experts, the digesters could accommodate the projected loadings throughout the planning period based on Colorado Spring projections and until 2020 based on El Paso County projections.

The blended sludge pump station and the DLD system including the area for screenings and grit (with higher loading rates on the DLD), have adequate capacity throughout the planning period.

Recommended Improvements to the Solids Handling, Treatment, and Disposal System The following issues have contributed to the recommendations for system improvements presented herein:

§ Biological action in the Sludge Transmission Main (Sludge Main) is causing an unusually large buildup of struvite in the digesters. § While significant yearly growth in biosolids to be treated is expected to continue, the projected loadings vary greatly depending on the success of regionalization.

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§ The capacity of the DLD area at the SHDF is limited by the soil’s ability to dissipate moisture. § The FSBs are near capacity, and should be expanded. To address these and other issues, the improvements listed below are recommended:

§ Increase the sludge flow rate to the SHDF to 700,000 gpd to reduce biological action in the Sludge Main and prevent struvite buildup. § Install a thickening system for the influent sludge to remove excess water caused by increasing sludge flow rate. § Build two additional FSBs. § Evaluate the effects of tilling the DLD surfaces on increasing evaporation. § Improve the grease handling system. The recommended improvements will provide treatment capability for projected loadings, while maintaining flexibility to meet uncertain future requirements. Figure ES-1 illustrates the components of the system, which are described below.

Grease Handling Improvements The existing grease/scum handling system for material from the Las Vegas Street WWTF includes collection in a heated concentrator and transfer to an unheated tanker truck. When the truck is full, the congealed grease is transported to the SHDF, where the truck is heated to liquify the grease. When the grease becomes liquid, it is quickly transferred into the digesters, causing a surge in gas production.

The recommendation for an improved system includes a new tanker truck, so liquid grease can be transferred slowly. Also, provisions should be made at the Las Vegas Street WWTF to apply steam or hot water to the tanker’s heating coils. If the grease is kept warm, it can be transferred starting immediately. At Clear Spring Ranch, provisions will be made to transfer grease at a measured rate. Also, the ventilation must be improved in the SHDF grease building to better protect worker health.

Raw Sludge Thickening/Centrate Treatment For planning purposes, thickening centrifuges are the recommended process due to the characteristics of the solids arriving at the SHDF (fermented, low pH, and extremely odorous). Therefore, the thickening process would need to be fully contained to contain odors. In addition, thickening centrifuges can be converted to function as dewatering centrifuges, but this should be investigated further and discussed during pilot testing. This conversion would allow dewatering capability should a Recirculating Fluidized Bed Boiler (RFBB) be installed in the future at the Ray Nixon Power Plant.

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Figure ES-1. Modified or Improved FSB/DLD System

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An upflow anaerobic sludge blanket reactor is recommended for centrate treatment. The centrate would be pumped through a packaged, skid mounted system. The process would consistently remove high levels of COD and nitrogen compounds before the treated centrate flows to the FSBs for polishing.

The Lower Fountain Water Reclamation Facility (LFWRF) is a proposed wastewater treatment facility currently being planned for the southern Colorado Springs Metropolitan Area to treat flows from the Jimmy Camp Creek Basin. Preliminary results of the ongoing Siting Study indicated that the Clear Spring Ranch area is the most favorable location for the LFWRF. Should this new WRF be constructed at Clear Spring Ranch, separate treatment at the SHDF would not be necessary to treat the centrate produced from the thickening centrifuges, accordingly, the LFWRF would need to be designed to accept and treat the centrate flows.

Digestion Modifications At some time in the future, depending on the condition of the equipment, conversion of the four existing digester covers to submerged-fixed type and from an unconfined gas lance mixing system to a mechanical draft tube mixing system is recommended. A structural integrity review of the digesters should occur to determine the need for the cover replacement, to accommodate mixing improvements, and to identify structural improvements. Cover conversion is recommended due to the age of the floating covers, and to provide foam control, automated mixing control, and increased reliability.

It is recommended to perform a pilot test to add iron chloride at the Las Vegas Street WWTF Blended Sludge Pump Station (BSPS) for struvite control. Colorado Springs Utilities staff is testing sludge to confirm if phosphate solubilization during Sludge Main travel is the cause of the extraordinary struvite scale deposits in the digesters.

FSB Expansion In order to remain under the design FSB loading rate of 20 lbs. VS / 1,000 ft2 / day, two additional FSBs will be needed (10 FBSs in service, 1 being dredged). It is also assumed that the dredge will need to be rehabilitated during the planning period.

Improved and Modified DLD System Tillage on the DLD acreage and other improvements can be used to increase evaporation and therefore increase the current biosolids slurry application rate of 7 inches/year. Testing should be performed to determine an appropriate tillage schedule and determine increased evaporation rates. One TerraGator should be added during the planning period. If tillage is successful, no additional DLD acreage is recommended.

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Water Management Recommendations include pumping more water to the SHDF for processing reasons. The water generated from thickening (i.e., centrate) must be treated before the water can be used elsewhere. After treatment, the centrate can be conveyed to the FSBs, where additional biological treatment occurs naturally. The water from these operations eventually flows to the supernatant ponds.

At this time, and for purposes of planning, it is assumed that an irrigation system at Clear Spring Ranch will be implemented to handle the excess water that would otherwise build up at the SHDF.

Implementation of the Preferred System Figure ES-2 depicts the proposed implementation schedule for the preferred system, and associated costs. The schedule could be affected if population growth and loadings vary from what is currently anticipated.

It should be noted that estimated costs for the alternatives were initially evaluated in Chapter 7 and then were refined in Chapter 11 for the recommended alternative.

The recommended improvements depicted in the proposed implementation schedule reflect a total expenditure of approximately $25 Million over the next 13 years. Figure ES-3 outlines the proposed projects to be implemented, which all occur through the year 2016.

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Component Estimated Year Cost 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025

Projected Average Raw Sludge Loading -- (City-Based), dry tons per day 45.70 49.00 52.40 55.80 59.10

Projected Average FSB Loading (Digester -- Discharge) (City-Based), dry tons per day 25.60 27.40 29.30 31.20 33.10 Projected DLD Loading (City-Based), -- tons per year 7,000 7,500 8,000 8,500 9,000 Pilot Test: Iron Chloride at BSPS for Struvite Control $200,000 Grease Handling Improvements $350,000 Sludge Thickening Pilot Tests (Centrifuge and GBT) $250,000 Sludge Thickening 1 $8,600,000 Centrate Treatment 2 $2,690,000 Study to evaluate aquifer production capability $80,000 Irrigation System 2 $1,420,000 Structural Integrity Review of Digesters 1 to 4 $20,000 Digester Improvements (Units 1 to 4) 3 $7,210,000 FSB Expansion $3,630,000 FSB Dredge Rehabilitation $130,000 DLD Tillage Testing 4 $100,000 DLD Injection Equipment 4 $230,000 Recommended Improvements $24,910,000 1 Should the RFBB be installed in 2008, potential conversion of thickening centrifuges to dewatering or partial dewatering centrifuges would occur in 2007-2008. A cost for this conversion is not included. 2 Should the LFWRF be constructed at the Clear Spring Ranch site, centrate treatment and irrigation may not be necessary, depending on timing of plant construction. The LFWRF should be designed to accept/treat the centrate flows if constructed at Clear Spring Ranch. 3 Timing based on results of Structural Integrity Review. 4 A DLD tillage study is recommended in 2004 to determine tillage potential and proper equipment selection. If tillage is successful, DLD tillage equipment purchase is recommended in 2005- 2006. Costs for the tillage equipment not included. One TerraGator is recommended during the planning period for future increased loading (cost included-2015).

Figure ES-2. Expected Cost Disbursement

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$7,000,000 2005 and 2006: Includes Design and Construction for Thickening System (partial), Centrate Treatment, Includes Digester Water Management System, and Grease Handling Improvements Improvements (Units 1 to 4 (year $6,000,000 2)) Includes Pilot Testing and/or Studies for Includes Construction of Chemical Addition at Thickening System (year 2) Includes Additional BSPS, Sludge $5,000,000 TerraGator for DLD Thickening, Aquifer Includes Design and System Production Capability, Construction of Digester Digester Structural Includes Design and Improvements (Units 1 to Integrity Review, and Construction of 2 4) (Timing Dependent on $4,000,000 DLD Tillage Field Trials Additional FSBs Structural Integrity Review)

$3,000,000 Annual Projected Expenditure

$2,000,000

Includes Rehab of FSB Dredge

$1,000,000

$0 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Year Figure ES-3. Program Capital Expenditures

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Chapter 1. Background

Overview The Colorado Springs Utilities Clear Spring Ranch Solids Handling & Disposal Facility (SHDF) is designed for the collection, stabilization, storage, and disposal of all sewage sludges (biosolids) produced at the Las Vegas Street Wastewater Treatment Facility (WWTF). The SHDF Masterplan uses previously completed studies and reports along with an in-depth evaluation of the existing facilities to develop a comprehensive Masterplan. Clear Spring Ranch is located in El Paso County, and consists of approximately 5,000 acres.

Colorado Springs Utilities operates the Las Vegas Street WWTF. The plant consists of two separate secondary treatment processes that are served by a common headworks, primary treatment, disinfection, and point of discharge. The two secondary treatment processes are the activated sludge process (referred to as the advanced wastewater treatment or AWT plant) and the trickling filter/solids contact process (referred to as the bioplant). The facility currently treats average daily flows of approximately 48 million gallons per day (mgd). Under the current configuration, the combined capacity of both of the treatment processes is 65 mgd to meet the anticipated chronic effluent ammonia concentrations. The AWT process is rated at 47 mgd and the bioplant process is rated at 18 mgd.

The Northern Water Reclamation Facility (NWRF) is expected to start up in 2005. The first phase of the NWRF will have a capacity of 20 mgd, expandable to 30 mgd.

Purpose of Study Several issues are causing Colorado Springs Utilities to reassess its sludge processing system at the SHDF. These include the following:

§ Flow of biosolids to the facility seems higher than projected. § Capacity may be reached sooner than expected. § Current operational issues may affect efficiency. § Potential for SHDF to become a regional facility. § Future regulations regarding biosolids use/disposal. § Use/disposal opportunities for biosolids. § Ability of the site to accommodate future needs.

Study Scope The major objective of this planning effort was to develop an economical and flexible biosolids management plan that will meet future needs. Therefore, the primary objectives of this SHDF Masterplan are as follows:

§ Quantify current and future biosolids treatment capacity needs.

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§ Re-evaluate capacity of existing facility. § Plan to meet future regulatory needs. § Optimize existing facilities as well as review new technologies and practices. § Identify current and future environmental issues. § Identify and schedule improvements for infrastructure and operations.

This Masterplan documents the evaluations, conclusions, and recommendations related to the SHDF at Clear Spring Ranch.

Existing System The facilities at the SHDF currently consist of eight anaerobic digesters, the digester equipment building, an energy recovery building, dedicated land disposal (DLD) areas, a pumping/ maintenance building, nine facultative sludge basins (FSB), and two supernatant lagoons. An expansion of these facilities was completed in early 2000. The expansion project included four new digesters and three new FSBs as the major improvements. The SHDF has had a history of excellent performance. Since start-up, the facility has consistently met treatment objectives and has been recognized as a well managed and efficient operation.

The SHDF is located about 17 miles southwest of downtown Colorado Springs. As described in the Supernatant Management Plan and Zero Discharge Treatment Evaluation (October 1998), the facility became operational in 1984 and serves as a disposal site for the following materials.

§ Fly ash from the R.D. Nixon Power Plant located north of the SHDF on the Clear Spring Ranch site and the Drake Power Plant near downtown. § Brine from the Zero Discharge Treatment Facility located on the Clear Spring Ranch site, which treats blowdown from the power plant and recycles it back to the cooling towers. § Sludge, screenings, and grit from the Las Vegas Street WWTF.

The following is a brief description of the major processes associated with the SHDF.

Blended Sludge Pump Station The blended sludge pump station (BSPS) is located at the Las Vegas Street WWTF. This pump station handles a combination of primary and secondary sludges from the activated sludge train and pumps them to the SHDF.

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Sludge Transmission Main The Sludge Transmission Main (Sludge Main) conveys the sludge from the BSPS to the SHDF. The 14-inch diameter pipeline extends for 17.6 miles and has a capacity of about 700,000 gallons per day (gpd).

Anaerobic Digesters Prior to the 1998 expansion, there were four anaerobic digesters at the SHDF. The piping and valving were arranged to allow blended sludge to be pumped from the wetwell to any or all of the digesters. The four new anaerobic digesters were constructed to operate in parallel with the original digesters.

Facultative Sludge Basins The purpose of the FSBs is to store, stabilize, thicken, and reduce the volume of solids. The FSBs function with a high degree of reliability, economy, and flexibility. The FSBs are operationally reliable because capacity exists to function satisfactorily under many possible adverse conditions such as: power failure, flooding, peak loading, equipment failure, weather extremes, and maintenance shutdowns. Before the 1998 expansion, there were six FSBs at the SHDF. Three new FSBs were constructed as part of the expansion. These operate in parallel with the previously existing units. The FSBs are long-term storage units that typically process and store the sludge solids for an average of three to five years before it is transferred to the DLD for final disposal.

Dedicated Land Disposal The DLD operation is designed to achieve final disposal of biosolids by subsurface soil injection. The DLD system at Clear Spring Ranch totals approximately 194 acres with an additional 15 acres for grit and screening waste disposal. An additional 36 acres are being added to the system in 2004. The DLD sites are designed to provide permanent disposal of biosolids dredged from the FSBs. A floating dredge is used to pump harvested sludge from the FSBs to the Operations Building Wetwell. DLD circulation pumps discharge the harvested sludge to a piping network routed through the DLD areas. A high flotation tire tank truck with subsurface injection equipment (TerraGator) takes the sludge from the loading stations in the DLDs and injects it into the soil.

Site Water Management The original design concept for the supernatant generated at the SHDF was to dispose of it through evaporation from the supernatant lagoons and, if necessary, pump excess water back to the Las Vegas Street WWTF. Over the past 15 years of operation, evaporation rates have not always been sufficient to keep up with the supernatant generation and precipitation at the facility. The combination of supernatant and precipitation in excess of the evaporation rate is termed “excess water.” No piping of excess water back to the Las Vegas Street WWTF has been implemented.

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Planning Organization Colorado Springs Utilities authorized Brown and Caldwell to begin work on the SHDF Masterplan on November 1, 2002. The planning effort has been a joint endeavor between Colorado Springs Utilities’ and Brown and Caldwell’s staffs. The following ten technical memoranda were drafted and reviewed throughout the project.

1. Technical Memorandum No. 1 containing solids projections (quality and quantity; i.e., raw sludge) for the study interval. 2. Technical Memorandum No. 2 describing the capacity of the existing system and operations, with identification of bottlenecks. 3. Technical Memorandum No. 3 describing existing and potential future regulatory requirements. 4. Technical Memorandum No. 4 describing beneficial use and disposal options. 5. Technical Memorandum No. 5 describing the identification and evaluation of options to meet future regulatory and capacity requirements. 6. Technical Memorandum No. 6 describing the options for using digester gas for energy production. 7. Technical Memorandum No. 7 containing results from the environmental evaluation. 8. Technical Memorandum No. 8 describing the siting of the alternatives. 9. Technical Memorandum No. 9 containing identification and evaluation of recommended alternatives for future facility improvements. 10. Technical Memorandum No. 10 containing Capital Improvement Plan/Financial Plan and detailed project information sheets describing each proposed project.

A number of meetings and workshops were conducted throughout the period of time during which the report was developed. The purpose of the meetings and workshops was to discuss the various sludge related issues and technical memoranda findings and make decisions regarding sludge management at Clear Spring Ranch. These meetings and workshops assisted with achieving a consensus regarding the various components of the SHDF Masterplan.

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Chapter 2. Solids Projections

Introduction To establish a long-range sludge use/disposal program, it is necessary to estimate the quantities of sludge that are anticipated in the future. Sludge quantity and quality will determine the size of treatment facilities and use/disposal site requirements which may affect the feasibility of various management alternatives.

This chapter summarizes the sludge projections and identifies the assumptions that formed the basis of the projections. Historical data for this Masterplan has been obtained from previous studies or reports and from Colorado Springs Utilities staff.

Projections The projections presented are based on available information and are subject to many factors that can influence the actual amount of sludge produced. Future sludge quantities are closely related to population projections for the Colorado Springs area and El Paso County over the next 20-25 years. Some industrial activities can also impact sludge quantities. It will be necessary to review and update these projections every five years to confirm or modify the projections and to evaluate the impact of these changes on the constructed facilities at the SHDF.

Projected Population Population projections for this Masterplan were obtained for local and regional levels of treatment. The City of Colorado Springs historical population values (1990-2001) were provided by the State Demographers Office (April 2003). Colorado Springs projected population (2002-2025) is taken from Colorado Springs Utilities internal projections, which were derived from the El Paso County Global Insight (September 2002) forecasts. Colorado Springs projections include Manitou and Peterson Field. The El Paso County historical and projected population was obtained from Global Insight (September 2002). Entities included in the El Paso County forecasts include Colorado Springs, Calhan, Fountain, Green Mountain Falls, Manitou Springs, Monument, Palmer Lake, and Unincorporated El Paso County. Projections through the year 2025 are listed below in Table 2-1 and Figure 2-1. No effort was made to delineate service areas or recalculate the population for this Masterplan.

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Table 2-1. Comparison of Recent Population Projections For The Colorado Springs Area and El Paso County Year Colorado Springs a El Paso County b 1980 215,105 311,855 1985 248,123 370,340 1990 280,430 395,961 1995 328,782 469,660 2000 360,890 519,716 2005 390,958 565,876 2010 419,312 609,279 2015 448,237 653,554 2020 479,979 697,550 2025 505,691 741,500 a Colorado Springs historic (1990-2000) values were provided by the State Demographers Office (April 2003). Colorado Springs projected population (2005-2025) are Colorado Springs Utilities internal projections, which were derived from the El Paso County Global Insight (September 2002) forecasts. 1990 and 2000 population are April 1 values. 1995 is a July 1 value. Values for 1980 and 1985 were obtained from the WISP. b The El Paso County historic and projected population was provided by Global Insight (September 2002).

Notes: 1. For Comparison, projections listed in the 1997 Basis of Design Memorandum list a 1996 base population of 340,698 and a high population of 341,810 and 2006 base population of 407,343 and high population of 424,758. 2. For Comparison, projections listed in the April 1980 Long-Range Sludge Management System Facility Plan for the population contributing to the Las Vegas Street WWTF in 2000 are 420,985 and 578,850 in 2020.

In 2000, El Paso County had approximately 159,000 more people than Colorado Springs. As shown on Figure 2-1, the non-City population within the County will rise approximately 236,000 in 2025. Projections should be monitored closely and adjusted if Clear Spring Ranch decides to receive sludge from other entities within the County. It is recommended that the Colorado Springs projections should be the basis for the capacity analysis at the local level and the El Paso County values should be the basis for regional planning.

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Figure 2-1. Comparison of Historic Population and Projections for the Colorado Springs Area and El Paso County

Future flow projections are related to future service population, so if the population changes, the wastewater flows at the Las Vegas Street WWTF will change accordingly. Table 2-2 and Figure 2-2 display the historical and projected annual average and maximum month flows to the Las Vegas Street WWTF for the Colorado Springs area and projected flows for El Paso County.

Table 2-2. Historic and Projected Flows to the Las Vegas Street WWTF Colorado Springs 1 El Paso County 2 Annual Average Maximum Month Flow, Annual Average Maximum Month Year Flow, mgd mgd Flow, mgd Flow, mgd 1980 24.5 27.9 1985 28.6 34.8 1990 33.3 36.1 1995 44.4 54.5 2000 45.5 48.3 2001 44.7 47.5 2002 42.1 43.2 2005 47.0 52.5 68.1 76.0 2010 50.4 56.3 73.3 81.9 2015 53.9 60.2 78.6 87.8 2020 57.4 64.1 83.9 93.7 2025 60.8 67.9 89.2 99.6 1 Historical (1980-2002) annual average and maximum month flows were obtained from the Las Vegas Street WWTF. Projected annual average flows (2005-2025) are based on Colorado Springs Utilities internal population

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projections, which were derived from the El Paso County Global Insight (September 2002) forecasts and a flow production factor of 120 g/c/d (based on average of historical data from 1980, 1985, 1990, 1995, 2000, 2001, and 2002). Projected maximum month flows are calculated based on a maximum month to annual average peaking factor of 1.12 also based on the average of historical data. 2 Projected annual average flows (2005-2025) are based on projected population from Global Insight (September 2002) and a flow production factor of 120 g/c/d (based on average of historical data from 1980, 1985, 1990, 1995, 2000, 2001, and 2002). Maximum month flows are calculated based on a maximum month to annual average peaking factor of 1.12 also based on the average of historical data.

Figure 2-2. Historical and Projected Flows for the Colorado Springs Area and El Paso County

Projected Raw Sludge Production The historical sludge values for 1990, 1995, 2000, 2001, and 2002 are listed in Table 2-3. Values for both the BSPS at the Las Vegas Street WWTF and influent to Clear Spring Ranch are displayed to show differences in sludge quantities due to hydrolysis and fermentation (first stages of anaerobic digestion) in the long Sludge Main.

The historical sludge values have been increasing since 1990, as shown in Table 2-3. Significant increases have occurred in the past few years. The values of 0.27 pounds per capita per day (p/c/d) and 0.23 p/c/d were used to project sludge quantities for the two population sources at the BSPS and influent to Clear Spring Ranch, respectively.

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Table 2-3. City of Colorado Springs Historical Sludge Production Ann. Annual Average Blended Sludge Avg. Pump Station Sludge at Las Vegas Annual Average Digester Influent Sludge at Flow Street WWTF (Dry Weight) Clear Spring Ranch (Dry Weight) Year Population1 mgd p/c/d ppd pounds/MG p/c/d ppd pounds/MG 1990 280,430 33.3 0.17 48,103 1,445 0.16 46,046 1,383 1995 328,782 44.35 0.21 68,128 1,536 0.17 57,033 1,286 2000 360,890 45.52 0.24 85,752 1,884 0.21 76,303 1,676 2001 369,853 44.65 0.26 97,000 2,172 0.23 86,458 1,936 2002 375,123 42.09 0.27 102,229 2,429 0.22 83,5402 1,985 1 Source: State Demographers Office (April 2003) for 1990-2001. Value for 2002 is a Colorado Springs Utilities internal projection, which was derived from the El Paso County Global Insight (September 2002) forecasts. 2 Average includes data from January through November 2002. ppd -pounds per day (dry weight basis) p/c/d - pounds per capita per day

The annual average sludge quantities anticipated to be generated by the Las Vegas Street WWTF are given in Table 2-4 for the Colorado Springs area and in Table 2-5 for El Paso County, respectively. Figure 2-3 and Figure 2-4 display the historical and estimated solids production from the two sources, the BSPS at Las Vegas Street WWTF and the digester influent at Clear Spring Ranch. The values in Table 2-3, Table 2-4, and Table 2-5 include all residential, commercial, and industrial sources. No attempt was made to differentiate these sludge quantities; commercial and industrial sludge quantities are assumed to be proportional to residential quantities. These quantities are projected using the population projections and the calculated per capita sludge production rate for 2002 for the BSPS (0.27 p/c/d) and 2001 for the digester influent sludge at Clear Spring Ranch (0.23 p/c/d), as shown in Table 2-3. These projection factors are the highest of the annual average values for the years shown. Projections were calculated by multiplying the current average pounds per capita per day by the projected population.

Table 2-4. City of Colorado Springs Annual Average Raw Sludge Projections Annual Annual Average Blended Sludge Average Pump Station Sludge at Las Vegas Annual Average Digester Influent Sludge Flow Street WWTF (Dry Weight) at Clear Spring Ranch (Dry Weight) Year Population 1 mgd p/c/d ppd pounds/MG p/c/d ppd pounds/MG 2005 390,958 47.03 0.27 106,544 2,266 0.23 91,392 1,943 2010 419,312 50.44 0.27 114,271 2,266 0.23 98,020 1,943 2015 448,237 53.92 0.27 122,154 2,266 0.23 104,781 1,943 2020 476,979 57.38 0.27 129,987 2,266 0.23 111,500 1,943 2025 505,691 60.83 0.27 137,812 2,266 0.23 118,212 1,943 1 Source: Colorado Springs Utilities internal projections, which were derived from the El Paso County Global Insight (September 2002) forecasts.

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Table 2-5. El Paso County Annual Average Raw Sludge Projections Annual Annual Average Blended Sludge Pump Average Station Sludge at Las Vegas Street Annual Average Digester Influent Sludge Flow WWTF (Dry Weight) at Clear Spring Ranch (Dry Weight) Year Population 1 mgd p/c/d ppd pounds/MG p/c/d ppd pounds/MG 2005 565,876 68.07 0.27 154,213 2,266 0.23 132,281 1,943 2010 609,279 73.29 0.27 166,041 2,266 0.23 142,427 1,943 2015 653,554 78.62 0.27 178,107 2,266 0.23 152,777 1,943 2020 697,550 83.91 0.27 190,097 2,266 0.23 163,061 1,943 2025 741,500 89.19 0.27 202,075 2,266 0.23 173,335 1,943 1 Source: Global Insight (September 2002).

250,000

200,000

150,000

100,000

50,000

Sludge Projections, Pounds per Day 0 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 Year Historical Blended Sludge Pump Station Sludge (City of Colorado Springs) Historical Influent Digester Sludge at Clear Spring Ranch (City of Colorado Springs) Projected Blended Sludge Pump Station Sludge (City of Colorado Springs) Projected Influent Digester Sludge at Clear Spring Ranch (City of Colorado Springs) Projected Blended Sludge Pump Station Sludge (El Paso County) Projected Influent Digester Sludge at Clear Spring Ranch (El Paso County) Figure 2-3. Historic and Projected Annual Average Sludge Values at the Las Vegas Street WWTF BSPS and Influent to the Digesters at the SHDF

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3,000

2,500

2,000

1,500 1997 Basis of Design, 1,460 pounds/MG 1,000

500 Pounds per Million Gallons

0 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 Year Historical Blended Sludge Pump Station Sludge Historical Influent Digester Sludge at Clear Spring Ranch Projected Blended Sludge Pump Station Sludge Projected Influent Digester Sludge at Clear Spring Ranch 1997 Basis of Design (1,460 ppd/MG) Figure 2-4. Historic and Projected Annual Average Pounds per Million Gallons at the Las Vegas Street WWTF BSPS and Influent to the Digesters at the SHDF

The 1997 Basis of Design Memorandum for the 1998 improvements to Clear Spring Ranch estimated a value of 1,460 pounds/MG of dry solids as a basis for projections. As shown above in Figure 2-4, this design value is low based on anticipated flows and population. Historical values for 2002 are higher at approximately 2,000 pounds/MG. This increase may be attributed to a reduction in I/I through pipeline improvement projects, changes to the AWT process, or other factors.

Thickened Sludge Production. In 1990, thickened sludge production was 48,000 ppd at the Las Vegas Street WWTF. In 1995, thickened sludge production increased 42 percent to about 68,000 ppd (average). From 2000 to present, thickened sludge quantities have been steadily increasing. An explanation for the higher sludge quantities can be attributed to an increase in population, addition of the AWT process, better data collection, and perhaps combinations of these and other factors.

The thickened sludge quantity projection factor is 0.27 p/c/d leaving the Las Vegas Street WWTF BSPS and 0.23 p/c/d arriving at the SHDF. Assuming this "per capita" loading will remain the same through the year 2025, the total sludge quantities produced will increase over the planning period based on the population projections. The total amount of sludge for use/disposal will increase from a current (2002) 83,500 pounds of dry solids per day to about 118,200 pounds of dry solids per day in the year 2025 for Colorado Springs as shown in Table 2-4. As shown in Table 2-5, the 2025 projected sludge for El Paso County is expected to reach 173,300 pounds per day.

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Solids Production Trends. Table 2-6 provides a comparison of other facilities similar in flow and type to the Las Vegas Street WWTF. Per capita values for thickened sludge range from 0.27 to 0.32 p/c/d.

Table 2-6. Solids Quantities Comparison to Similar Facilities Annual Annual Average Thickened Population Average Flow, Sludge Facility Served mgd g/c/d ppd p/c/d Wichita, KS (1997) 330,997 41.1 124 105,000 0.32 Colorado Springs, CO (2002) 375,123 42.1 112 102,200 0.27 1 Littleton/Englewood, CO (2000) 247,000 25.5 103 67,500 0.27 1 Due to hydrolysis and fermentation in the sludge pipeline, the 2002 sludge is reduced from 102,200 to 83,530 pounds per day, resulting in 0.21 p/c/d for the sludge arriving at Clear Spring Ranch. g/c/d - gallons per capita per day ppd - pounds per day p/c/d - pounds per capita per day

The projected values used for the City of Colorado Springs are consistent with similar facilities and seem reasonable for planning purposes. While the projections in Table 2-1 provide a basis for final sludge use/disposal evaluations, these projections do not provide the level of detail required for individual process evaluations. Therefore, further analysis of the existing sludge quantities within the SHDF are conducted in Chapter 3 to determine loadings on various processes.

Projected Grit and Screenings Future screenings and grit quantities are estimated using an average production rate of 7.1 cubic feet of material per million gallons of raw wastewater at the Las Vegas Street WWTF. This production rate is based on 2002 actual data and is for dewatered grit and screenings. In 2002, the annual average flow at the Las Vegas Street WWTF was 42.1 mgd and the screenings and grit conveyed to Clear Spring Ranch from the Las Vegas Street WWTF was 3,027 cubic yards (cy). An additional 1,000 cy was received from the collection system, totaling 4,027 cy in 2002.

To estimate future quantities of grit and screenings using these rates, it is necessary to use estimated total wastewater flow generated in the City of Colorado Springs. The wastewater flow multiplied by the estimated projection rate equals the projected quantity. Table 2-7 and Table 2-8 gives estimated future grit and screenings quantities for the two population sources.

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Table 2-7. Estimated Future Screenings and Grit Quantities (Based on Colorado Springs Population) Annual Average Year Population Flow, mgd Screenings and Grit (cy/d) 2 2002 375,123 42.1 11.01 2005 390,958 47.0 12.3 2010 419,312 50.4 13.2 2015 448,237 53.9 14.1 2020 476,979 57.4 15.0 2025 505,691 60.8 15.9 1 In 2002, screenings and grit conveyed to Clear Spring Ranch from the Las Vegas Street WWTF was 3,027 cy/yr. An additional 1,000 cy/yr was received from the collection system, totaling 4,027 cy in 2002. 2 Screenings and Grit production based on 7.1 cf/mg and projected flows (2002) for Las Vegas Street WWTF.

Table 2-8. Estimated Future Screenings and Grit Quantities (Based on El Paso County Projected Population) Annual Average Year Population Flow, mgd Screenings and Grit (cy/d) 1

2005 565,876 68.1 17.8

2010 609,279 73.3 19.2

2015 653,554 78.6 20.6

2020 697,550 83.9 22.0

2025 741,500 89.2 23.4

1 Screenings and Grit production projections based on 2002 data (7.1 cf/mg and projected flows from the Las Vegas Street WWTF).

Projected Scum Future scum quantities are estimated using a production rate of approximately 3,700 pounds per day or 88 pounds per million gallons of wastewater. This production rate is based on 2002 actual data. In 2002, the annual average flow at the Las Vegas Street WWTF was 42.1 mgd and 170,000 gallons per year of scum was measured. Scum is estimated by Clear Spring Ranch staff to contain 90 percent grease and 10 percent water. To estimate future quantities of scum using this rate, it is necessary to use the estimated wastewater flow generated in the City of Colorado Springs. The wastewater flow multiplied by the estimated production rate equals the projected quantity. Table 2-9 and Table 2-10 gives estimated scum quantities for the two population sources.

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Table 2-9. Estimated Scum Quantities (Based on Colorado Springs Population) Annual Average Year Population Flow, mgd ppd cy/d1 2002 375,123 42.1 3,691 2.3 2005 390,958 47.0 4,599 2.9 2010 419,312 50.4 5,012 3.1 2015 448,237 53.9 5,576 3.5 2020 476,979 57.4 6,172 3.9 2025 505,691 60.8 6,750 4.2 1 Scum production based on 2002 actual value of 170,000 gallons per year. Specific gravity of scum is estimated at 0.95 (EPA Process Design Manual, Sludge Treatment and Disposal, September 1979).

Table 2-10. Estimated Scum Quantities (Based on El Paso County Projected Population) Annual Average Year Population Flow, mgd ppd cy/d1 2005 565,876 68.1 5,968 3.7 2010 609,279 73.3 6,426 4.0 2015 653,554 78.6 6,893 4.3 2020 697,550 83.9 7,357 4.6 2025 741,500 89.2 7,820 4.9 1 Scum production based on 2002 data (88 pounds per million gallons of wastewater).

Summary The Colorado Springs projections will be the basis for the capacity analysis at the local level and the El Paso County Population values will be the basis for regional planning. These population sources and associated sludge projections will be used as a basis to evaluate the existing capacity of the major processes at the SHDF in Chapter 3.

The need for Capital Improvements Projects (CIP) will be based on actual loadings. Colorado Springs Utilities should track annual actual loadings and adjust the CIP schedule accordingly. CIP recommendations will be provided at the local level as well as the regional level.

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Chapter 3. Evaluation of the Capacity of the Existing System and Operations

Introduction The primary objective of this analysis was to evaluate the existing capacity of the major process units at the SHDF. Therefore, the primary components of this evaluation are as follows:

§ Review the design criteria for current treatment unit sizing and capacity included in the 1997 Basis of Design Memorandum. § Identify any additional information, which may affect the rated capacity of the plant (e.g., new pump, abandoned tank, operational bottlenecks). § Evaluate the capacity of each major treatment unit by evaluating process performance and the last two years of operating data. § Compare/evaluate capacity with projected loads. § Identify and prioritize bottlenecks in the process train for future conditions.

Description of Major Process Units The following sections describe the major processes at the SHDF.

Blended Sludge Pump Station The BSPS is located at the Las Vegas Street WWTF. This unit handles a combination of primary and secondary sludges from the activated sludge process train. The BSPS is equipped with 3 piston diaphragm pumps that convey the sludge to the SHDF. Each pump has a capacity of 175 gpm at an average solids concentration of approximately 3.1 percent (dry solids).

Sludge Main The Sludge Main conveys the sludge from the BSPS at the Las Vegas Street WWTF to the SHDF. The 14-inch and 10-inch diameter pipeline extends for 17.6 miles and has a capacity of about 700,000 gpd.

Anaerobic Digesters There are a total of eight digesters at the SHDF. The four older digesters have a volume of 1.4 million gallons each and are equipped with floating covers. The four newer units were built as part of the facility expansion, which began in 1998 and was completed in early 2000. These four newer digesters are equipped with submerged-fixed covers and have a volume of 1.8 million gallons each.

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All the digesters are operated as primary mixed units in parallel and are provided with a drainage pumping station that can be used for pumping the digested sludge to the FSBs, draining the digester tanks, or transferring sludge between tanks. Circulating sludge lines and pumps are provided for internal mixing and heating of sludge for each digester. The older digester’s mixing system utilizes recirculated digester gas for transmitting mixing energy to the digester content. The newer digesters are equipped with four draft tube mechanical mixers in each unit.

Facultative Sludge Basins (FSBs) The purpose of the FSBs is to store, stabilize, and reduce the volume of solids transported from the digesters prior to ultimate disposal in the dedicated land disposal area. The FBSs are long-term storage units that contain sludge solids for an average of three to five years before the harvested sludge is removed and land applied. The FSBs are 15-foot liquid depth basins with a surface area of 5 acres each (45 acres total), and are fed digested sludge 24 hours per day, 7 days per week. Before the 1998 expansion, there were six FSBs at the SHDF. Three new FSBs were constructed as part of the 1998 expansion. All FSBs operate in parallel. The main functions of the FSBs are:

§ Achieve substantial volatile solids reduction by long-term stabilization of solids. § Destroy maximum amount of solids so that less solids are dredged and disposed to the DLD areas. § Provide storage, particularly over the winter months when DLD operations are limited. § Provide pathogen reduction. § Thicken sludge to minimize liquid injected into DLD sites.

Dedicated Land Disposal (DLD) System The DLD operation is designed to achieve final land treatment and disposal of biosolids by subsurface soil injection. Subsurface soil injection of FSB-harvested sludge is one of the most environmentally acceptable methods of final land treatment and disposal because the sludge is incorporated directly with the soil, reducing exposure to the atmosphere. The DLD sites were established for the sole purpose of land treatment and disposal to meet the long-term needs of Colorado Springs Utilities and are designed to provide permanent disposal of the sludge removed from the FSBs.

A total of 194 acres of the Clear Spring Ranch site is presently used for the DLD system with an additional 15 acres for grit and screening waste disposal. An additional 36 acres are being added to the system in 2004. It is anticipated that the DLD system will remain in service as the long-term means of ultimate sludge disposal, unless other disposal means are required or become economically attractive. The DLD operation has provided an extremely cost effective means of sludge disposal for Colorado Springs Utilities.

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Supernatant Handling System The supernatant from the FSBs flows by gravity to two supernatant storage lagoons on the site. The lagoons are non-discharging to surface streams and supernatant disposal is achieved through evaporation. The total surface area of the supernatant lagoons is approximately 34 acres.

Process Design Criteria and Performance Table 3-1 summarizes the design criteria applied in sizing the major units of the SHDF. These criteria were established in the SHDF expansion Basis of Design Memorandum, dated May 8, 1997.

The performance data of the major solids treatment processes at the SHDF are presented in Table 3-1. The performance values for the units are based on 2001 and 2002 historical data provided by Colorado Springs Utilities staff.

Table 3-1. Process Design Criteria and System Performance for 2001 and 2002 Parameter Design Criteria 2001 2002 BSPS sludge solids concentration, percent (by wt) (MMF) 3.1 3.1 3.0 Digester hydraulic retention time, days (MMF)1 24 19 22 Digester volatile solids reduction, percent (MMF) 55 47 50 Digester solids loading rate, lb VSS / day / ft3 (MMF) 0.068 0.077 0.070 Digester feed sludge volatile solids fraction, percent (MMF) 80 80 80 Digested sludge TSS concentration, percent (by wt) (MMF) 1.85 1.85 2 FSB loading rate, lb VSS / 1000 ft2 / day (AA) 20 21 20 FSB harvested sludge solids concentration, percent (by wt) (AA) 5.0 5.3 4.0 1 15 days is required by CDPHE and EPA to achieve Class B quality. MMF= Maximum monthly flow AA= Annual Average Assumptions: 2001: 4 new digesters operating 2002: 2 old and 3 new digesters operating

From the results presented in Table 3-1, the digesters and the FSBs were operated at design capacity at the maximum monthly flow and annual average for 2001 and 2002.

The anaerobic digesters were operated over the maximum monthly flow hydraulic design criteria by 30 percent and 14 percent for 2001 and 2002, respectively. However, lower hydraulic detention times in the 20-day range are recommended in literature. In the case of solids loading rate to the digesters, they were operated over the design criteria basis by 24 percent and 6 percent for the same years. As mentioned previously, a higher solids loading rate value in the range of 0.1 lb/VSS/day/ft3 is typically found in digester design. The FSBs were operated on the upper limit range for the years 2001 and 2002 if compared to the design criteria of 20 lb VSS/1000 ft2/day annual average.

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An additional analysis was performed to observe the effect of higher solids concentrations in the influent of the anaerobic digesters. Solids concentrations ranging from 3.5 to 3.8 percent were used. The solids loading rate of 0.07 lb VSS/day/ft3 (2002 actual MMF) was used as a basis. Based on these assumptions, the solids concentration only affects the flow rate to the units since the solids loading is assumed as constant. As seen in Table 3-2, as the solids percentage in the influent increases, the hydraulic detention time of the digesters increases as well.

Table 3-2. Effects of Higher Solids Concentrations on Hydraulic Capacity in the Anaerobic Digesters 3% 3.5% 3.6% 3.7% 3.8% Anaerobic Digesters Solids Solids Solids Solids Solids Digester hydraulic retention time, days (MMF)* 22 29 29.5 30 31 * Based on the parallel operation of two (2) older and three (3) newer anaerobic digesters.

A sludge mass balance was performed at maximum monthly flow of 377,000 gpd (February 2002) to evaluate the maximum capacities of the major units of the SHDF. The results are summarized in. For the purpose of this analysis, the design criteria presented previously in Table 3-1 was adopted to facilitate the evaluation.

The major solids handling and disposal processes and their capacities are listed in Table 3-3. The results presented in this table show that most of the major process units at the SHDF are capable of treating the maximum monthly flow of 377,000 gpd. However, the limiting process seems to be the FSBs, with a maximum capacity of 38,848 lb VSS/day (based on 40 acres), which was already reached based on the annual average loading.

Table 3-3. Mass Balance Comparison Design Loading for Unit Operation Size/Capacity Capacity, ppd 2002, ppd Blended Sludge Pump Station 3 - Abel piston-diaphragm pumps, 400 psig, 75 hp., pumping 195,456 137,140 (MDF) 525 gpm blended sludge to the Clear Spring Ranch Facility 130,304 (a) 97,470 (MMF) Sludge Main 486 gpm 180,936 97,470 (MMF) Sludge Receiving Station Surge Tank - 74,000 gallons Surge Tank Recirc. Pump, WEMCO Model C Centrifugal pump, 570 137,140 (MDF) 570 gpm 212,210 gpm @ 19 ft. TDH, 10 HP 97,470 (MMF) Digester Feed Pumps - North digesters (older), 4 pumps, progressive 432 gpm cavity type, 108 gpm each, 58 ft. TDH. 137,140 (MDF) 384,211 Digester Feed Pumps, South Digesters (newer), 5, pumps, 97,470 (MMF) 600 gpm mechanical diaphragm, 120 gpm each, 60 ft. TDH, 7.5 HP

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Design Loading for Unit Operation Size/Capacity Capacity, ppd 2002, ppd Anaerobic Digesters 4 old digesters, 1.4 million gallons each, 85 ft. diameter, 33 ft. sidewater depth, floating cover, sludge removed by pumping from center well. 0.068 lb VSS/ ft3 99,993 (b) 77,936 (c) 4 new digesters, 1.8 million gallons each, 85 ft. diameter, 36 ft digester sidewater depth, submerged fixed cover; sludge removal is continuous flow over a weir into standpipe. Biogas Management System Low-pressure gas from all eight digesters passes through moisture separators and sediment traps before being routed to the boilers 156,000 scf/hr 156000 scf / hr 46,230 scf/hr and waste gas burners. Sludge Heating System The boilers provide digester heating and building heat. There are 4 29.4 Million 29.4 Million Btu / 29 Million Btu / boilers, 3 each at 250 HP, and 1 at 125 HP. The boilers can be Btu/h hr hr(d) fired on diesel fuel or digester gas. 1 - Sludge recirculation pump is provided for each digester, 500 500 gpm per NA NA gpm, 35 ft. TDH, 15 HP. digester in use The digester heating system has a total of 8 heat exchangers, with a 20.4 Million NA NA capacity of 2.55 million BTU/h each. Btu/h The heat reservoir system consists of two hot water recirculating Rated 540 gpm, pumps - one duty and one standby, pumping at 540 gpm, with 5 but maximum NA NA HP. flow 1300 gpm Facultative Sludge Basins (FSBs) The 9 FSBs are each 675 x 316 feet, with a maximum liquid depth of 20 lb VSS / 1,000 20 lb VSS / 1,000 22.4 lb VSS / 15 feet. They have a combined surface area of 45 acres. ft2 ft2 (e) 1,000 ft2 (f) There are 3 harvested sludge pumps, each capable of 750 gpm at 134 118,336 (AAF) 2250 gpm 1,351,080 ft. TDH with 75 HP 200,600 (MDF) Dedicated Land Disposal Injection Capacity (DLD) There are 194 acres in the DLD system. They are served by a system 3,700 gal/ 127 dry 31 tons/acre/year of piping that carries the harvested sludge from the FSBs to stations injector/ trip tons/acre/year (g) (h) where the TerraGators are refilled with sludge for injection. Supernatant Handling System Lagoon no. 1 - 13 acres NA NA Lagoon no. 2 - 23 acres (a) Based on two pumps in operation and one standby (b) Capacity based on four old digesters and three new digesters (c) Observed capacity based on actual operation in year 2002; 2 old and 3 new digesters, a loading rate of 0.074 lb VSS/d/ft3 (d) Observed capacity based on 600 Btu / ft3 (Metcalf & Eddy, 1991) (e) Capacity based on total FSB area of 40 acres (f) Calculated capacity based on an actual sludge feed rate of 38,988 lb VSS / day (g) Capacity based on 3 injectors, and 25 loads/day at 6 percent dry solids concentration (h) Based on year-round operation in the year 2002 Notes: MDF= maximum daily flow MMF= maximum monthly flow AAF= annual average flow

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Projected Capacity The projected solids loading rates to the SHDF are presented in Figure 3-1, and were calculated based on two different population sources obtained from Chapter 2. The projected capacities for the major units with the exception of the digesters, were calculated based on the projected loading rates and the design criteria presented in the Basis of Design Memorandum, dated May 8, 1997.

200,000 180,000 160,000 140,000 120,000 100,000 80,000 60,000 40,000 20,000 Projected Solids Loading Rate, lb/day 0 2000 2005 2010 2015 2020 2025 2030 Time, Years

Colorado Springs El Paso County Figure 3-1. Projected Annual Average Solids Loading Rate to the SHDF

Blended Sludge Pump Station The maximum capacity of the BSPS is based on all three pumps in service. This is the maximum amount of sludge flow that can be conveyed to the SHDF. Figure 3-2 shows that the BSPS could convey the raw sludge to the SHDF until approximately the year 2025 for both the Colorado Springs and El Paso County-based projected loadings. The flows were calculated assuming a 3.1 percent blended sludge solids concentration.

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900,000

800,000

700,000

600,000

500,000

400,000

300,000 Projected Flow, gpd 200,000

100,000

0 2000 2005 2010 2015 2020 2025 2030 Time, Years

Capacity Colorado Springs El Paso County

Figure 3-2. Blended Sludge Pump Station – Capacity vs. Projected Flows (3.1% Solids)

Anaerobic Digesters The projected digester capacity was calculated based on the parallel operation of four older and three newer digesters, for a total of seven units with a total active volume of 11 million gallons. The projected loading rates presented in Figure 3-1 were peaked by a factor of 1.14 (obtained by dividing the peak week solids loading rate by the maximum monthly solids load). This calculated peak week solids loading rate was used to estimate the expected capacity of the digesters. The VSS fraction was taken from the design criteria presented in Table 3-1.

If the solids loading rate follows the expected growth pattern displayed in Figure 3-1, the anaerobic digester capacity could be exceeded in 2020 for the Colorado Springs based projections shown on Figure 3-3. The digesters appear that they cannot handle the projected solids loading rate based on El Paso County projections at the present time.

Although the foregoing analysis indicates a lack of capacity over time, the solids loading rate established in the design criteria from the Basis of Design Memorandum seems to be low compared with common values found in literature. Normal solids loading rate values vary between 0.12 and 0.16 lb/ft3/d at peak loading rates; therefore, it is recommended to use a design solids loading rate on the order of 0.1 lb/ft3/d. If this is the case, the capacity of the digesters could be extended throughout the planning period for Colorado Springs based projections and until 2020 for El Paso County based projections as displayed on Figure 3-3.

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0.12

0.1 lb VSS/ft3/day 0.1

0.08 0.068 lb VSS/ft3/day 0.06

0.04

0.02 Solids Loading Rate, lbVSS/ft3/day

0 2000 2005 2010 2015 2020 2025 2030 Time, Years

Design Capacity Colorado Springs El Paso County Recommended Capacity Figure 3-3. Anaerobic Digesters – Capacity vs. Projected Solids Loading Rate (Peak Week)

A hydraulic analysis was performed on the anaerobic digesters based on the retention time established in the process design criteria, Table 3-1. For the purpose of this analysis, four older and three newer digesters, with a total active volume of 11 million gallons, were assumed to operate in parallel. The influent flow was determined by using the projected solids loading rates presented in Figure 3-1 and a sludge concentration of 3.1 percent solids. These results are presented in Figure 3-4. This figure shows that the hydraulic capacity, in terms of mgd, should accommodate Colorado Springs’ projected flows throughout the planning period, while exceeding El Paso County-based flows in 2005.

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0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1 Influent Flow to Anaerobic Digesters, mgd

0.0 2000 2005 2010 2015 2020 2025 2030 Time, Years

Colorado Springs El Paso County Capacity Figure 3-4. Anaerobic Digesters – Hydraulic Capacity vs. Projected Flows (Peak Week)

Facultative Sludge Basins The maximum capacity of the FSBs was based on a total active area of 40 acres, leaving the remaining 5 acres available for maintenance, harvesting or emergency situations. The design criteria of 20 lb VSS/1,000 ft2/day was used to establish the maximum annual loading rate for this process. As previously described, the FSBs have been operated at design capacity during at least 2001 and 2002, as displayed in Table 3-1 and Table 3-4. Therefore, as seen in Figure 3-5, the FSBs cannot handle the projected solids load expected in the future from the El Paso County-projected loadings. Based on Colorado Springs-projected loadings, the capacity of the FSBs (20 lb VSS/1000 ft2/day) could be exceeded in 2010.

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40

30

20 lb VSS/1000 ft2/day

10

0 Solids Loading Rate, 2000 2005 2010 2015 2020 2025 2030 Time, Years

Capacity Colorado Springs El Paso County

Figure 3-5. Facultative Sludge Basins – Capacity vs. Projected Loading

Dedicated Land Disposal (DLD) In practice, evaporation from the surface of the DLDs has been shown to be the dominant mechanism which limits the harvested sludge injection rate. During the year 2002, approximately 38 million gallons of sludge at an average of 3.99 percent solids by weight were injected in the DLD system at a loading rate of 25 to 30 loads/day, which resulted in 32 tons of dry solids/acre for the year. City-based projections are expected to reach 46 dry tons/acre in 2025 and County projections are estimated at 68 dry tons/acre in 2025 (Figure 3-6). It is difficult to determine DLD loading capacity. A value of 60 dry tons/acre/yr was assumed, however, further evaluation is required to confirm the actual DLD loading limit. DLD tillage is recommended to increase evaporation and application rate.

A 36-acre DLD expansion is expected to be complete in 2004. This project began after performing this capacity analysis; therefore, this area was not accounted for during this study. This area will provide additional capacity and therefore increase the life expectancy of the DLD system at the SHDF.

According to the design criteria established in the Basis of Design Memorandum, the DLD injection system handles sludge from the FSBs at 6 percent solids by weight, at a solids injection rate of 3,700 gal/injector, with a total of four injectors; however, this sludge concentration has been observed to be 5.3 percent and 4 percent for 2001 and 2002, respectively. The number of injectors used varies depending on the time of the year and injection loads, but according to the plant staff, four machines are used from March to October, and three machines are used during the rest of the year, from November to February.

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80 70 Further evaluation required to confirm actual DLD capacity loading limit 60 50 40 30 20 10 0 Solids Loading Rate, Dry Tons/acre/year 2000 2005 2010 2015 2020 2025 2030 Time, Years

Capacity Colorado Springs El Paso County

Note: Capacity is estimated at 60 dry tons/acre/year. This value needs to be confirmed through recommended DLD tillage testing. Figure 3-6. Dedicated Land Disposal – Capacity vs. Projected Loading (based on 194 acres)

Capacity Summary The major solids handling and disposal processes and their capacities are shown in the previous figures. Since 2001, the FSBs have been operated at the design capacity established in the Basis Design Memorandum, dated May 8, 1997, and appear to be the limiting process.

Table 3-4 presents a performance summary based on volatile solids (VS) removal at the SHDF. This analysis is based on the Van Kleek Method and the average performance data for 2000, 2001, and 2002. This table shows the VS removal (percentage) in the Sludge Main, the anaerobic digesters, and the FSBs. According to the data, an average of 70 percent of volatile solids were removed during operation.

Table 3-4. VSR Reduction Summary Component Sludge Main Digesters FSBs VS Removal - Each Process, % 9 50 34 Cumulative VS Removal % 9 55 70 Notes: 1. Values based on a combined average of data for 2000, 2001, and 2002. 2. Based on 1,000 mg/L.

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The anaerobic digesters are the second limiting process at the SHDF. The capacity analysis revealed the digesters should be able to treat projected solids until approximately 2020, based on the Colorado Springs projections, and through 2005, based on El Paso County projections. Capacity is based on the design criteria presented in Table 3-1 and the information shown in Figure 3-3. However, if the solids loading rate is increased to 0.1 lb VSS/ft3/day as recommended, the digesters could accommodate the projected loadings throughout the planning period based on Colorado Springs projections and until 2020 based on El Paso County projections. Finally, the blended sludge pump station and the DLD system, including the area for screenings and grit, have adequate capacity throughout the planning period.

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Chapter 4. Existing and Potential Future Regulatory Requirements

Overview The objectives of this chapter are to present current regulations and discuss proposed requirements that could affect the SHDF. Future regulatory requirements should be accommodated by building flexibility into the facility improvements, which will be considered during the alternatives analysis and incorporated in the recommendations. The following items will be discussed in this chapter.

§ Existing air and biosolids disposal regulatory requirements. § Likely future changes to the federal, state, regional, and local regulations and anticipated future monitoring and reporting requirements.

The consideration of how future regulations would likely affect the alternatives being considered for Colorado Springs Utilities will be accomplished in Chapter 6.

This Masterplan utilizes previously completed studies and reports. Some of the existing regulatory information was obtained from the 2001 Wastewater Infrastructure Strategic Plan (WISP).

Air Quality Requirements This section lists applicable air emission permits, describes air emission issues at the SHDF, and discusses key features of relevant regulations. Permitted emissions from wastewater facilities under the federal Clean Air Act and/or the Colorado Air Quality Control Act are displayed in Table 4-1.

Table 4-1. Permitted Air Emissions Tons/Year Carbon Volatile Organic Nitrogen Monoxide Hydrogen Particulate Compounds Facility Sulfite (SO2) Oxides (NOX) (CO) Sulfide (H2S) Matter (PM) (VOC) Solids Handling Disposal Facility Permit 186.4 lbs/hr (3 3.5 tons/mo., 8.9 tons/mo., 0.7 tons/mo., 0.6 tons/mo; 0.1 tons/mo., 95EP0093 hr avg), 4.4 41.4 tons/yr 105.7 tons/yr 8.1 tons/yr 6.1 tons/yr PM10 1.1 tons/yr tons/mo., 52.5 = 0.5 tons/mo, tons/yr 5.0 tons/yr Fugitive 0.34 (95EP1098) – Reporting only Title V Operating Permit Application on file with agency (Facility ID 0410091) Las Vegas Street WWTF Permit 3.1 tons/mo., 1.6 tons/mo., 3.5 tons/mo., 95EP1097 36.0 tons/yr 19.1 tons/yr 41.7 tons/yr (modified)

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The SHDF is one of several air emission sources included within the contiguous boundary of the Clear Spring Ranch property. Other sources include the Ray D. Nixon Power Plant, a gravel mining operation, three permitted solid waste disposal sites, and intermittent activities associated with the disposal of confiscated explosives by the police department.

For permitting purposes, the SHDF is considered to be a “major source” because all sources at the Clear Spring Ranch facility are collectively considered when assessing impacts to National Ambient Air Quality Standards and Prevention of Significant Deterioration (PSD) incremental increases.

Physical and/or process changes to the SHDF are considered by the CDPHE as “major modifications” if the changes result in significant net emission increases. For purposes of PSD, the values in Table 4-2 display considered levels of significance.

Table 4-2. Significant Net Emissions Increase Pollutant Significant Net Emissions Increase (tons/year) SO2 40 NOX 40 PM 25 PM10 15 CO 100 H2S 10

Impacts to National Ambient Air Quality Standards are also considered whether or not the source is considered major.

The Las Vegas Street WWTF is not at this time considered a major source. It is currently permitted under a “Synthetic Minor” permit. The permit establishes federally enforceable limits to its emissions allowing for this classification. Although future expansions are not anticipated at this time to trigger major modification issues, any proposed construction would require an amendment to the current air emissions permit prior to beginning construction or process modifications if the change results in an increase in emissions.

Major modification issues to any facility would trigger the following PSD provisions:

§ Conduct Top-down Best Available Control Technology (BACT) analysis for any pollutant for which there is a significant increase and implement appropriate control measures. § Conduct air dispersion modeling and possible ambient air quality monitoring to demonstrate that the project will not cause a violation of ambient air quality standards.

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§ Conduct Visibility Impairment modeling and assess impacts to Class I areas. This would include Florissant Fossil Beds (National Monument). § Contact Federal Land Managers within 200 kilometer radius of source for review and input.

BACT for CO control is typically considered to be proper combustion techniques or catalytic converters installed in the ducts or stacks. BACT for NOX control is expected to be installation of Lo-NOX boiler burners or lean-burn cogeneration engines. BACT for control of SO2 emissions associated with digester biogas combustion would involve techniques or strategies for reducing the H2S concentration in the biogas. This may include iron sponge, chemical treatment, enzyme treatment or chemical scrubbing.

Other rules affecting air emissions from the SHDF and Las Vegas Street WWTF are listed in the Colorado Air Quality Control Commission (AQCC) regulations, particularly Regulations 1, 3, 6, and 8.

The following federal requirements (some of which are adopted by reference in state regulations) have the potential to apply to the SHDF and/or the Las Vegas Street WWTF:

§ NSPS Subpart Dc: Standards of Performance for small industrial-commercial- institutional steam generating units. This NSPS focuses on boilers fueled by coal and oil, and the only requirement for gas-fired boiler is to provide the regulatory agency with an advanced notification of basic information such as fuel type and construction and startup dates.

§ NSPS Subpart KKK: Standards of Performance for equipment leaks of VOC from onshore natural gas processing plants. This NSPS could potentially apply to the SHDF expansion if the selected biogas management option is to produce pipeline quality gas. However, the NSPS is intended to apply to well-site natural gas operations and would not logically apply to the SHDF.

§ Clean Air Act (CAA) Title III Maximum Achievable Control Technology (MACT) Standards: MACT standards were established for public owned wastewater treatment systems. These standards establish technology-based standards for controlling emissions of listed Hazardous Air Pollutants (HAPs) from facilities classified as major sources. Major sources of HAPs are defined as sources or facilities which emit or have the potential to emit 10 tons per year or more of any one listed HAP or 25 tons per year or more of any combination of HAPs. A federally enforceable permit can be used to limit emissions and avoid this requirement. The SHDF is collocated with other sources which are major sources of HAPs. Because of this, the Colorado Department of Public Health and Environment considers the SHDF a major source of HAPs. Currently, there are no promulgated MACT

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standards that would apply to the SHDF. However, discussion of a pending boiler MACT follows.

§ Pending Boiler Maximum Achievable Control Technology (MACT) Standards: Currently, regulation under 40 CFR 63 Subpart DDDDD, National Emission Standards for Hazardous Air Pollutants (NESHAP) for Industrial/Commercial/Institution Boilers and Process Heaters, have been proposed by the USEPA. This regulation is also referred to as the Boiler MACT. The intent of this regulation is to reduce emissions of HAPs and applies to boilers and process heaters located at facilities which are major sources of HAPs. As written, sources with boilers or process heaters subject to this regulation will be required to monitor either emissions of particulate matter or metals. Sources subject to Subpart DDDDD will be required to demonstrate continuous compliance with the proposed regulation.

§ Turbine NSPS for Microturbines: The federal New Source Performance Standard; 40 CFR 60 Subpart GG, applies to Stationary Gas Turbines with a heat input at peak load equal to or greater than 10 million Btu per hour which began construction or were modified or reconstructed after October 3, 1977. New turbines subject to this requirement must conduct an initial performance test to verify compliance with Nitrogen Oxide emissions limits. Emission units subject to Subpart GG must also monitor nitrogen and sulfur content in fuel. The turbines at the SHDF have no potential to exceed the energy limit, so this standard does not affect future operations.

§ Colorado New Source Performance Standard for Fuel Burning Equipment: Regulation 6, Part B, Section II.C provides standards for all fuel burning equipment constructed, reconstructed or modified after January 30, 1979. Emission units subject to this requirement must meet a particulate matter standard of 0.5 pounds per million Btu per hour total heat input. The SHDF has PM limits for the boilers that are more restrictive than this regulation, therefore, Regulation 6, Part B, Section II requirements for fuel burning equipment are satisfied. Regulation 6, Part B, Section II.D.3 limits sulfur dioxide emissions from combustion turbines. This regulation requires that all combustion turbines, including the SHDF microturbines, limit sulfur dioxide emissions to 0.8 pounds per million Btu of heat input.

Endangered Species Act The Endangered Species Act (ESA) of 1973 as amended, requires that “Each federal agency shall ensure that any action authorized, funded, or carried out by such agency is not likely to jeopardize the continued existence of any endangered species or threatened species or result in the destruction or adverse modification of habitat.” Under the ESA, no person may “take” a species listed as

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threatened or endangered without a permit. The act is administered by, and permits are issued by, the United States Fish and Wildlife Service (FWS) under the United States Department of Interior (DOI) and the National Marine Fisheries Service (NMFS) under the auspices of the United States Department of Commerce. “Take” is defined as harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct a species listed under the ESA as Endangered or Threatened. Harm is further defined to include significant habitat modification or degradation that results in death or injury to listed species by significantly impairing essential behavior patterns, including breeding, feeding, or sheltering. Destruction or disruption of habitat of a listed species can, under certain circumstances, result in the take of such species.

For action that occurs without Federal involvement, such as activities that occur on private holdings, incidental take permits are issued under Section 10(a) of the ESA. Among other things, an applicant for a permit must develop a Habitat Conservation Plan (HCP) for approval by the USFWS defining the potential for take of threatened and/or endangered species and planned mitigation and conservation measures. The USFWS assesses the proposed take which may result from the proposed activities and assesses the adequacy of the proposed HCP to ensure that the species will continue to be conserved in a Biological Opinion (BO) prior to issuance of a permit.

When a project involves action by any federal agency, whether to approve, fund or otherwise support a private action or to carry out a federal project, and where the action may have an affect on a federally listed species or designated critical habitat, the federal agency is required under Section 7(a)(2) of the ESA to consult with the FWS. Depending on the outcome of consultation, the FWS will prepare a Biological Opinion or letter of concurrence evaluating the proposed federal action and its potential to result in a take of listed species and jeopardize the survivability of the species. The Project subject to the federal action may proceed if the FWS issues a statement finding that the action will not jeopardize the survivability of the species. However, the federal agency must implement and enforce any conditions imposed by the FWS in the statement. Impacts to proposed critical habitat would require a conference with FWS to determine appropriate conservation measures.

In order to determine the federally listed species that may be located on or within the vicinity of any project area, the FWS is contacted and a list of species that the action may affect should be requested. Such contact initiates informal consultation with the FWS. During the period of informal consultation, a Biological Assessment (BA) will be completed. If this time period extends beyond 180 days informal consultation should be re-initiated and a new list requested (generally if 90 days passes an updated species list is requested). The BA should address all species listed or proposed for listing under the Endangered Species Act as well as all critical habitat listed or proposed for listing.

Formal consultation is initiated with the USFWS if the results of the BA indicate that an adverse affect on a species will occur. Under formal consultation, measures will be documented that will ensure the continued well being of the species. At the end of a successful formal consultation period, a Biological Opinion will be issued by the FWS and the project will be allowed to proceed from an ESA standpoint.

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The FWS lists 10 Endangered animals and 6 Endangered Plants and 8 Threatened animals and 7 Threatened plants for the state of Colorado under the ESA. Additionally there are two animal species whose population in Colorado are designated as Experimental non-essential. It is not likely that all listed species for the state occur in any one region of the state, however there is potential for the need to address several of these for a given project depending on it’s geographic size. All listed species for the state of Colorado are shown Table 4-3.

Table 4-3. Colorado Endangered Species Common Name Scientific Name Designation Grizzly Bear Urus arctos horribilis T Uncompahgre Fritillary Butterfly Boloria acrocnema E Bonytail Chub Gila elegans E Humpback Chub Gila cypha E Whooping Crane (except where XN) Grus americana E Whooping Crane Grus americana XN Bald Eagle Haliaeetus leucocephalus T Black-footed Ferret (except where XN) Mustela nigripes E Black-footed Ferret Mustela nigripes XN Southwestern Willow Flycatcher Empidonax traillii extimus E Canada Lynx Lynx canadensis T Preble’s Meadow Jumping Mouse Zapus hudsonius preblei T Mexican Spotted Owl Strix occidentalis lucida T Colorado Pikeminnow (except Salt and Verde R.) Ptychocheilus lucius E Piping Plover Charadrius melodus T Pawnee Montane Skipper Hesperia leonardus montana T Razorback Sucker Xyrauchen texanus E Least Tern (interior population) Sterna antillarum E Greenback Cutthroat Trout Oncorhynchus clarki stomias T Gray Wolf (except where XN) Canis lupus E Mancos Milk-vetch Astragalus humillimus E Osterhout Milk-vetch Astragalus osterhoutii E Clay-loving Wild Buckwheat Eriogonum pelinophilum E Penland Alpine fen Mustard Eutrema penlandii T Colorado Butterfly Plant Gaura neomexicana coloradensis T Dudley Bluffs Bladderpod Lesquerella congesta T Knowlton Cactus Pediocactus knowltonii E Penland Beardtongue Penstemon penlandii E North Park Phacelia Phacelia formosula E Dudley Bluffs Twinpod Physaria obcordata T Uinta Basin Hookless Cactus Sclerocactus glaucus T Mesa Verde Cactus Sclerocactus mesae-verdae T Ute Ladies’-tresses Spiranthes diluvialis T

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The Colorado Natural Heritage Program (CNHP) lists 2 Endangered animals and no Endangered Plants, and 5 Threatened animals and 1 Threatened plant for El Paso County, Colorado under the ESA. All listed species for the County of El Paso, Colorado are shown in the table below. Known occurrences according the CNHP that lie within a five mile radius of the project area are identified in the column titled “5 Mile Radius” in Table 4-4.

Table 4-4. El Paso County Endangered Species 5 Mile Common Name Scientific Name Designation Radius Whooping Crane (except where XN) Grus americana E No Bald Eagle Haliaeetus leucocephalus T Yes Black-tailed Prairie Dog Cynomys Ludovicianus C Yes Black-footed Ferret (except where XN) Mustela nigripes E No Preble’s Meadow Jumping Mouse Zapus hudsonius preblei T No Swift Fox Vulpes velox E Yes Mountain Plover Charadrius montanus P Yes Mexican Spotted Owl Strix occidentalis lucida T Yes Greenback Cutthroat Trout Oncorhynchus clarki stomias T No Ute Ladies’-tresses Spiranthes diluvialis T No

On July 30, 1998, the National Wildlife Federation (NWF) filed a petition with the FWS to list the black-tailed prairie dog (Cynomys ludovicianus) as “threatened” under the ESA. On February 4, 2000, FWS published a notice in the Federal Register summarizing its 12-month Administrative Findings on the petition, within which it was cited that the species “warrants listing”, but that higher priority species deserving of more immediate attention “precludes the listing of the black-tailed prairie dog at this time” (a.k.a., a “warranted but precluded” finding). So, for now, the species is officially considered a federal candidate for listing, and FWS will review its status every 12 months. What this federal action has stimulated, though, is a response by the various states that make up the historic range of the black-tailed prairie dog to voluntarily develop conservation strategies for the species. The FWS expects that state-implemented conservation programs will both forestall eventual listing and promote recovery of the black-tailed prairie dog.

State Sensitive Species While the ESA is not designed to proactively protect state listed or state sensitive species, Section 9(a)(2)(B) prohibits the violation of state laws regarding state protected species. State sensitive species other than those already listed in the ESA section, that CNHP lists within El Paso County, are shown in the Table 4-5. Known occurrences according the CNHP that lie within a five-mile radius of the project area are identified in the column titled “5-Mile Radius”.

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Table 4-5. El Paso County – State Sensitive Species 5-Mile Common Name Scientific Name Designation Radius Peregrine Falcon Falco peregrinus anatum S2B, SZN Yes Ferruginous Hawk Buteo regalis S3B, S4N No Greater Sandhill Crane Grus canadensis tabida S2B, S4N No Long-billed Curlew Numenius americanus S2B, SZN No McCown’s Longspur Calcarius mccownii S2B, SZN No Ovenbird Seiurus aurocapillus S2B, SZN No Tiger Beetle Cicindela nebraskana S1 No Colorado Blue Euphilotes rita coloradensis S2 No Cross-line Skipper Polites origenes S3 No Dusted Skipper Atrytonopsis hianna S2 No Hops Feeding Azure Celastrina humulus S2 No Moss’s Elfin Callophrys mossii schryveri S2 No Simius Roadside Skipper Amblyscirtes simius S3 No Common Hog-nosed Skunk Conepatus leuconotus SH Yes Gunnison’s Prairie Dog Cynomys gunnisoni S5 No Townsend’s Big-eared Bat Plecotus townsendii pallescens S2 No Arkansas Darter Etheostoma cragini S2 No Sedge Carex oreocharis S1 No Alpine Bluebells Mertensia alpina S1 No American Currant Ribes americanum S2 No Bird-bill Day Flower Commelina dianthifolia S1 No Bristle-stalk Sedge Carex leptalea S1 No Clawless Draba Draba exunguiculata S2 No Common Moonwort Botrychium lunaria S2 No Crawe Sedge Carex crawei S1 No Dwarf Wild Indigo Amorpha nana S2 No Eaton’s Lip Fern Cheilanthes eatonii S2 No Gay Feather Liatris ligulistylis S1 No Golden Blazing Star Nuttalia chrysantha S1 No Golden Columbine Aquilegia chrysantha rydbergii S1 No James Telesonix Telesonix jamesii S2 No Narrowleaf Grapefern Botrychium lineare S1 No New Mexico Cliff Fern Woodsea neomexicana S2 No Pikes Peak Spring Parsley Oreoxis humilis S1 No Plains Ragweed Ambrosia linearis S3 No Porter Feathergrass Ptilagrostis porteri S2 No Prairie Goldenrod Unamia alba S2 No Prairie Violet Viola pedatifida S2 No Purple Cliff-brake Pellaea atropurpurea S2 No

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5-Mile Common Name Scientific Name Designation Radius Rattlesnake Fern Botrypus virginianus europaeus S1 No Richardson Alum Root Heuchera richardsonii S1 No Rocky Mountain Bladder Pod Lesquerella calcicola S2 No Rocky Mountain Columbine Aquilegia saximontana S3 No Round-leaf Four-O’clock Oxybaphus rotundifolius S2 No Sandhill Goosefoot Chenopodium cycloides S1 No Selkirk Violet Viola selkirkii S1 No Small-headed Rush Juncus brachycephalus S1 No Southern Rocky Mountain Cinquefoil Potentilla ambigens S1 No White Adder’s-Mouth Malaxis monophyllos brachypoda S1 No Yellow Lady’s-slipper Cypripedium calceolus parviflorum S2 No Massasauga Sistrurus catenatus S2 No Triploid Colorado Checkered Whiptail Cnemidophorus neotesselatus S2 Yes

State rankings legend: S1 - State critically imperiled; typically 5 or fewer occurrences; S2 - State imperiled; typically 6 to 20 occurrences; S3 - State vulnerable; typically 21 to 100 occurrences; S4 - State apparently secure; usually > 100 occurrences; S5 - State demonstrably secure; S#S# - A range between two of the numeric ranks indicates uncertainty about the rarity of the element in the state; NR - Unranked; element is not yet ranked in the state; SU - Unrankable; not enough information is known; SH - Historically known with hopes of rediscovery; SX - Extinct; unlikely to be rediscovered; SE - An exotic established in the state; native to a nearby region; SA - Accidental; includes species (usually birds or butterflies) recorded once or twice or only at very great intervals, hundreds or thousands of miles outside their usual range; SR - Reported in the state, but not confirmed; SZ - Zero occurrences; typically refers to nonbreeding bird populations; B - Rank refers to the breeding population of the element; N - Rank refers to the nonbreeding population of the element; C - Element is extant only in captivation or cultivation; *Other factors, in addition to the number of occurrences, may be considered when assigning a state rank

The Migratory Bird Treaty Act of 1918 and subsequent amendments (16 U.S.C. 703-711) provides for the establishment of a Federal prohibition, unless permitted by regulations, to "pursue, hunt, take, capture, kill, attempt to take, capture or kill, possess, offer for sale, sell, offer to purchase, purchase, deliver for shipment, ship, cause to be shipped, deliver for transportation, transport, cause to be transported, carry, or cause to be carried by any means whatever, receive for shipment, transportation or carriage, or export, at any time, or in any manner, any migratory bird, included in the terms of this Convention . . . for the protection of migratory birds . . . or any part, nest, or egg of any such bird". A list of those protected birds can be found in 50 C.F.R. 10.13. These birds generally include any bird that migrates beyond United States boundaries into Canada, Mexico, Japan or Russia and excludes certain game birds. Executive Order issued January 11, 2001 further defines the responsibilities of the Federal Agencies to protect migratory birds. If construction must occur during the breeding season of migratory birds, (dates for specific bird species are usually determined by the FWS) the plan area should be surveyed for nests prior to implementation. If a migratory bird nest is found during construction with nestlings present, the area must be avoided until birds fledge. Surveys for nests should be conducted for existing and future areas where land will be disturbed. During the course of regular operation of an existing facility, if circumstances arise that warrant a depredation permit, a permit may be obtained from the FWS. “A Migratory Bird Depredation Permit authorizes certain management and control activities necessary to provide for human health and safety, protect personal property, or allow resolution of other injury to people or

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property. No permit is required merely to scare or herd depredating migratory birds other than endangered or threatened species and bald or golden eagles. A depredation permit is intended to provide short-term relief from migratory bird depredation until long-term measures can be implemented to reduce or eliminate the depredation problem through non-lethal control techniques (Migratory Bird Treaty Act, 50 CFR 21.41). A depredation permit is not usually issued during the construction phase of a project.

Biosolids Disposal and Utilization Issues Biosolids disposal at the SHDF is authorized under a CD issued by the El Paso County Planning Commission and Commissioners, and the Colorado Hazardous Materials and Waste Management Division. The CD addresses many land uses for the property, while a separate CD addresses power generation at the R.D. Nixon Power Plant. Alternatives to current disposal will be considered in facilities planning efforts. Federal regulations described below are applicable to both dedicated disposal and recycling as a soil amendment.

Federal Sludge Regulation Requirements (40 CFR, Part 503) and Current Sludge (Biosolids) Characteristics The EPA 503 rule gives direction to four basic areas: pollutant concentrations, pathogen reduction, vector attraction reduction, and management practices. Class A and Class B levels of pathogen reduction are recognized. A Class A biosolid is the highest quality material and has very few site constraints. To be considered a Class A product, specific treatment and testing requirements must be met. Table 4-6 summarizes the Class A requirements.

Table 4-6. Summary of the Six Process Alternatives for Meeting Class A Pathogen Requirements Alternative 1: Thermally Treated Biosolids must be subjected to one of four time- Biosolids temperature regimes. Alternative 2: Biosolids Treated in a Biosolids must meet specific pH, temperature, and air- High pH-High Temperature Process drying requirements. Alternative 3: Biosolids Treated in Demonstrate that the process can reduce enteric viruses Other Processes and viable helminth ova. Maintain operating conditions used in the demonstration after pathogen reduction demonstration is completed. Alternative 4: Biosolids Treated in Biosolids must be tested for pathogens – Salmonella sp. or Unknown Processes fecal coliform bacteria, enteric viruses, and viable helminth ova – at the time the biosolids are used or disposed, or, in certain situations, prepared for use or disposal. Alternative 5: Biosolids Treated in a Biosolids must be treated in one of the Processes to PFRP Further Reduce Pathogens (PFRP) (see Table 4-8). Alternative 6: Biosolids Treated in a Biosolids must be treated in a process equivalent to one of Process Equivalent to a PFRP the PFRPs, as determined by the permitting authority.

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In addition to the six alternatives given in Table 4-6, there are performance testing requirements for all Class A products shown in Table 4-7.

Table 4-7 Pathogen Requirements for All Class A Alternatives The following requirements must be met for all six Class A pathogen alternatives. Either: § The density of fecal coliform in the biosolids must be less than 1,000 most probable numbers (MPN) per gram total solids (dry-weight basis), or § The density of Salmonella sp. bacteria in the biosolids must be less than 3 MPN per gram total solids (dry-weight basis). Pathogen reduction must take place before or at the same time as vector attraction reduction, except when the pH adjustment, percent solids vector attraction, injection, or incorporation options are met

As noted in Table 4-6, Alternative 5, there is a series of Processes to Further Reduce Pathogens (PFRPs) that can produce the needed pathogen reduction to achieve Class A standards. They are given in Table 4-8.

Table 4-8. Processes to Further Reduce Pathogens (PFRPs) Listed in Appendix B of 40 CFR Part 503 1. Composting. Using either the within-vessel composting method or the static aerated pile composting method, the temperature of the biosolids is maintained at 55 degrees Celsius or higher for 3 days. Using the windrow composting method, the temperature of the biosolids is maintained at 55 degrees Celsius or higher for 15 days or longer. During the period when the compost is maintained at 55 degrees Celsius or higher, the windrow is turned a minimum of five times. 2. Heat Drying. Biosolids are dried by direct or indirect contact with hot gases to reduce the moisture content of the biosolids to 10 percent or lower. Either the temperature of the biosolids particles exceeds 80 degrees Celsius or the wet bulb temperature of the gas in contact as the biosolids leave the dryer exceeds 80 degrees Celsius. 3. Heat Treatment. Liquid biosolids are heated to a temperature of 180 degrees Celsius or higher for 30 minutes. 4. Thermophilic Aerobic Digestion. Liquid biosolids are agitated with air or oxygen to maintain aerobic conditions, and the mean cell residence time of the biosolids is 10 days at 55 to 60 degrees Celsius. 5. Beta Ray Irradiation. Biosolids are irradiated with beta rays from an accelerator at dosages of at least 1.0 megarad at room temperature (ca. 20 degrees C.) 6. Gamma Ray Irradiation. Biosolids are irradiated with gamma rays from certain isotopes, such as Cobalt 60 and Cesium 137, at room temperature (ca. 20 degrees C.).

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7. Pasteurization. The temperature of the biosolids is maintained at 70 degrees C or higher for 30 minutes or longer.

Unlike Class A biosolids which are essentially pathogen free, Class B biosolids may contain some pathogens. As such, some site restrictions will be required that will prevent crop harvesting, animal grazing, or public access for a certain period of time until environmental conditions have further reduced pathogen levels. Three alternatives for Class B biosolids are given in Table 4-9.

Table 4-9. Summary of the Three Alternatives for Meeting Class B Pathogen Requirements Alternative 1. The Monitoring of Indicator Organisms Test for fecal coliform density as an indicator for all pathogens. The geometric mean of seven samples shall be less than 2 million CFUs per gram of total solids at the time of use or disposal. Alternative 2. Biosolids Treated in a PSRP Biosolids must be treated in one of the Processes to Significantly Reduce Pathogens (PSRP) (see Table 4-10). Alternative 3. Biosolids Treated in a Process Equivalent to a PSRP Biosolids must be treated in a process equivalent to one of the PSRPs, as determined by the permitting authority

Table 4-10 describes designated Processes to Significantly Reduce Pathogens (PSRPs) for Class B biosolids. Performance testing is not required if these process criteria are met.

Table 4-10. Processes to Significantly Reduce Pathogens (PSRPs) Listed in Appendix B of 40 CFR Part 503 1. Aerobic Digestion. Biosolids are agitated with air or oxygen to maintain aerobic conditions for a specific mean cell residence time at a specific temperature. Values for the mean cell residence time and temperature shall be between 40 days at 20 degrees C and 60 days at 15 degrees C. 2. Air Drying. Biosolids are dried on sand beds or on paved or unpaved basins. The biosolids dry for a minimum of 3 months. During 2 of the 3 months, the ambient average daily temperature is above 0 degrees C. 3. Anaerobic Digestion. Biosolids are treated in the absence of air for a specific mean cell residence time at a specific temperature. Values for the mean cell residence time and temperature shall be between 15 days at 35 degrees C to 55 degrees C and 60 days at 20 degrees C. 4. Composting. Using either the within-vessel, static aerated pile, or windrow composting methods, the temperature of the biosolids is raised to 40 degrees C or higher and maintained for 5 days. For 4 hours during the 5-day period, the temperature in the compost pile exceeds 55 degrees C. 5. Lime Stabilization. Sufficient lime is added to the biosolids to raise the pH of the biosolids to 12 after 2 hours of contact.

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Both Class A and Class B biosolids must also undergo treatment to reduce the disease risk that is associated with bringing pathogens into contact with vectors (flies, mosquitoes, birds, etc.) that may create additional human or livestock health risk. These treatments or processes, when possible, must be conducted in a time that would be at or before the time period for processes to meet Class A or B requirements. Table 4-11 gives Options for Meeting Vector Attraction Reduction.

Table 4-11. Options for Meeting Vector Attraction Reduction Option 1. Meeting 38 percent reduction in volatile solids content. Option 2. Demonstrate vector attraction reduction with additional anaerobic digestion in a bench-scale unit. Option 3. Demonstrate vector attraction reduction with additional aerobic digestion in a bench- scale unit. Option 4. Meet a specific oxygen uptake rate for aerobically digested biosolids. Option 5. Use aerobic processes at greater than 40 degrees C for 14 days or longer. Option 6. Alkali addition under specified conditions. Option 7. Dry biosolids with no unstabilized solids to at least 75 percent solids. Option 8. Dry biosolids with unstabilized solids to at least 90 percent solids. Option 9. Inject biosolids beneath the soil surface. Option 10. Incorporate biosolids into the soil within 6 hours of application to or placement on the land. Option 11. Cover biosolids placed on the surface disposal site with soil or other material at the end of each operating day. (Note: Only for surface disposal.) Option 12. Alkaline treatment of domestic septage to pH or above for 30 minutes without adding more alkaline material.

Metal Concentrations of Biosolids In addition to pathogen and vector attraction reduction, all biosolids must also meet limits for pollutant (trace metal) concentrations. If biosolids exceed the ceiling limits for one metal, the biosolids cannot be land-applied. Furthermore, all biosolids must meet either pollutant concentration limits, cumulative pollutant loading rate limits, or annual pollutant loading rate limits for these same metals. Annual rate loading limits apply to bagged biosolids. Cumulative loading limits are used when biosolids are within ceiling concentrations for all ten metals but one or more metals exceed the pollutant concentration limits.

Table 4-12 outlines the ceiling and pollutant concentration levels that must not be exceeded and the yearly values from Colorado Springs test data. Colorado Springs Solids Data listed in Table 4-12 was obtained from the WISP and represents the period 1992-1997. Colorado Springs Utilities should review recent available data and perform sampling for data not recorded, to verify with the concentrations listed in Table 4-12. The Colorado Springs data is below pollutant concentration limits for all metals with the possible exception of zinc. The local governing unit will decide if this warrants restricting land application to cumulative loading limits.

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Table 4-12. Comparison of Average Monthly Metals Concentrations to Part 503 Limits Pollutant Colorado Springs Solids Ceiling Concentration Concentration Data – Min. and Max. Pollutant (mg/kg) (mg/kg) (mg/kg) Arsenic 75 41 <2.0-20.1* Cadmium 85 39 13-24 Copper 4,300 1,500 780-1,000* Lead 840 300 180-270* Mercury 57 17 1.1** Molybdenum 75 -- 5.57** Nickel 420 420 33-210* Selenium 100 100 14-18.8** Zinc 7,500 2,800 2,000-2,900* * Solids Handling Data – Facultative Sludge Basins Monthly Averages (1997, 1996, 1995, 1994, 1993, 1992). **Grab samples – AWT – ASE Sludge (January-April 1997). One time sampling – not monthly average.

Site Restrictions/Management Practices for Class A or B Biosolids (503.14) Bulk biosolids, Class A or B, cannot be applied to land if it is likely to adversely affect a threatened or endangered species as listed under the Endangered Species Act or its critical habitat. The biosolids cannot be applied to agricultural lands or other similar sites if the site is flooded, frozen or snow- covered so that biosolids enter a wetland or other “waters of the U.S.” The biosolids cannot be applied to land that is 10 meters or less from a “waters of the U.S.” The biosolids shall be applied at a rate that is equal to or less than the agronomic rate (typically based on nitrogen).

Class B Additional Site Restrictions for Cropland The following site restrictions apply to cropland, if the biosolids meet Class B characteristics and not Class A:

§ Animals cannot graze on site for 30 days after application. § Public access to land with a high potential for public exposure shall be restricted for 1 year after application of the biosolids. § Public access to land with a low potential for public exposure shall be restricted for 30 days after application of the biosolids. If any crops, including feed crops, are grown on this land, additional site restrictions will apply. The biosolids must meet at least Class B requirements if it is to be land applied to any type of cropland.

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Monitoring Requirements for Sludge Application According to the 40 CFR 503.16(a) (1) monitoring of the biosolids for pollutants, pathogen densities, and vector attraction reduction must, at a minimum, occur annually. Depending on the volume of biosolids produced additional sampling may be required as outlined in Table 4-13.

Table 4-13. Monitoring Requirements for Biosolids Application Annual Sludge Production Average Sludge Production (dry metric tons/year) (dry tons/day) Annual Monitoring (times/year) <290 <0.87 1 290-1,500 0.87-4.5 4 1,500-15,000a 4.5-45 6 >15,000 >34 12 a Colorado Springs Utilities is currently in this Category. Future projections (through 2025) remain in this category.

Record Keeping and Reporting Record keeping requirements vary with the type of biosolids that are produced. In all cases, records must be maintained by the entity that prepares biosolids for land application and also the entity that actually applies the biosolids. In addition, someone must certify that 503 rules are being followed related to land application. The certification statement and pertinent records must be on file for a minimum of five years.

Some facilities may not have reporting requirements. All Class I treatment works, all treatment works serving a population of 10,000 or more, and treatment works with a 1 mgd or greater design flow have reporting responsibilities. Information describing the prior calendar year sludge disposition must be submitted to the permitting authority by February 19 of each year.

Other Considerations for Class A or B Biosolids Application If biosolids are brought to the Clear Spring Ranch site from other entities not currently in the system, there may be a change in the quality of the biosolids that could impact the feasibility of long term land application. The quality of biosolids from other treatment entities is not known, and may contain higher levels of metals than the biosolids currently handled at the SHDF. It will be important for proper industrial pretreatment programs to be implemented to maintain the current acceptable quality of the sludge handled at the SHDF. Most importantly, the CD and 503 permit would require modification to allow biosolids from other entities to be brought to Clear Spring Ranch.

Another potential consideration that may be associated with the land application of biosolids outside the current CD boundary is the permitting implications associated with the existing biosolids and wastewater permits. If biosolids are applied to areas outside of the current CD, amendments to both permits and/or the CD will be required. Biosolids can be applied outside the CD area and must comply with the Colorado Discharge Permit System permit for pollutant limitations (i.e., metals listed in Table 4-12 and pathogens) and other management requirements.

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Future Regulatory Considerations Revisions to the Part 503 rule are under consideration. Future limits for dioxin-like compounds may be imposed on biosolids land application. Risk assessment has indicated that an appropriate limit for dioxins plus co-planar PCBs would be 300 ng/kg (parts per trillion) TEQ. Dioxin limits are controversial with proponents arguing that dioxin has serious environmental and health implications. But surveys of biosolids sources around the US have demonstrated that this compound is not typically present in significant concentrations and risks are not great enough to merit regulation. For the present, agencies are advised to test for dioxin-like compounds and consider the impact of proposed regulations if levels exceed 30 ng/kg TEQ.

An additional pending issue, not related to the 503 rule, is the trend toward Class A biosolids processes to address public and local government concerns related to biosolids land application. If a shift away from the current land disposal operation is recommended as a result of facilities planning efforts, Class A processes should be a consideration.

State, Regional, And Local Regulations

State Regulations CDPHE adopted their regulations in accordance with EPA standards on November 2, 1993. All biosolids recycling and disposal programs must comply with state and federal regulations to protect the environment and public health. Some key items referenced in the land application program described by CDPHE, Water Quality Control Commission in Biosolids Regulation No. 64, (last update effective March 1, 2000) are as follows:

§ Provide to CDPHE a Letter of Intent for the use and distribution of biosolids for their review. § CDPHE shall issue Notice of Authorization for the Use and Distribution of Biosolids or deny the notice. § Obtain the nutrient and trace-metal composition of the biosolids. § Contact CDPHE to ensure that all necessary requirements are met for biosolids use.

The federal and state regulations on biosolids processing and use mandate that biosolids be applied at agronomic rates to balance uptake of nitrogen by crops with the potential for nitrate leaching to ground water. These regulations limit the accumulation of contaminants in biosolids-amended soil to levels that are not harmful to the health of humans and other biota.

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Regional Regulations Effective August 16, 2002, The EPA Region VIII issued NPDES general permits for facilities or operations that generate, treat, and/or use/dispose of sewage sludge by means of land application, landfill, and surface disposal in Region VIII (Colorado). Coverage under the general permits may be for one of the following categories:

§ Category 1 – Facilities/operations that generate and/or partially treat sewage sludge, but do not use/dispose of sewage sludge. § Category 2 – Facilities/operations that use/dispose of sewage sludge and may also generate and/or treat sewage sludge. § Category 3 – Wastewater Lagoon systems that need to land apply sewage sludge on an occasional, restricted basis.

Coverage under the general permit will be limited to one of the three categories, but coverage may be granted to one or more subcategories under Category 2. In applying for coverage under the general permit, the applicant will be required to specify under which category or subcategory coverage is being requested. The requirements in the permit for the use/disposal of sewage sludge are based primarily on 40 CFR 503. The State of Colorado has not been authorized as the permit authority for Federal facilities. Therefore, a separate general permit is being issued for Federal facilities in Colorado (that are not located on Indian country).

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Chapter 5. Options for Beneficial Use of Biosolids

Introduction The purpose of this Chapter is to evaluate options for biosolids beneficial use at the SHDF. Class A and other products are described and public acceptance and marketability of these products are discussed.

The ultimate use or disposal of the biosolids largely influences the selection of the solids treatment recommendations for the Masterplan. Consequently, identifying how the sludge will be used or disposed, especially if it is different than current practice at the SHDF, takes precedence and should be resolved early.

Below is a description of Class B and Class A pathogen reduction options initially discussed for potential use at Clear Spring Ranch. In addition, beneficial use studies and examples are provided. Treatment options and alternatives are evaluated in Chapter 6.

Beneficial Use – Class B It is important that Colorado Springs Utilities identify and investigate options to provide beneficial use of sludge. This section considers options that meet Class B pathogen levels, equivalent to the EPA’s Processes to Significantly Reduce Pathogens (PSRP).

The beneficial use options require that the products be maintained at a high quality with respect to contaminants. In addition to economic considerations, beneficial use options must satisfy the following four conditions:

1. They must be acceptable to CDPHE and the EPA and comply with all applicable regulations.

2. Sites for beneficial use must be evaluated for availability (taking into account site, climate, and other limitations).

3. Environmental and health risks must be sufficiently low to satisfy the public and all agencies having jurisdiction.

4. The necessary equipment, staff and resources must be readily available.

The following Class B beneficial use options were investigated and are described in the paragraphs below.

§ On-site land application – slurry (only for small portion of output) § Off-site land application – dewatered cake product

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§ Off-site land application – air dried product § Off-site landfill cover or land or mine reclamation

On-Site Land Application – Slurry Liquid sludge application could be a feasible beneficial use option for a small portion of system production. Liquid sludge would be harvested and land applied on-site at the SHDF at approximately 4- to 6-percent solids concentration (i.e., solids content dredged from the FSBs).

Liquid sludge has been previously applied on small portions of the site. This represents a “supplemental” beneficial use option for Clear Spring Ranch biosolids.

Off-Site Agricultural Land Application (Primarily Dewatered Cake) Agricultural land application can be conducted with both liquid and dewatered sludge materials. This would require dewatering of the biosolids by means of equipment such as a belt filter press, centrifuge, or similar equipment.

Sludge material applied to agricultural land should meet the following quality characteristics as defined by 40 CFR Part 503.

§ Vector attraction: Greater than 38-percent volatile solids reduction in anaerobic digestion. § Pathogen reduction: Class B. § Metal concentration: Levels are below pollutant ceiling concentrations and cumulative pollutant loading limits to the land can be met.

In addition, various physical and institutional issues affect the agricultural land application of sludge. These issues are described in detail in Chapter 4. Some site restrictions are described below.

§ Bulk biosolids, Class A or B, cannot be applied to land if it is likely to adversely affect a threatened or endangered species as listed under the Endangered Species Act or its critical habitat. § The biosolids cannot be applied to agricultural lands or other similar sites if the site is flooded, frozen or snow-covered so that biosolids enter a wetland or other “waters of the United States.” § The biosolids cannot be applied to land that is 10 meters or less from a “waters of the United States.” § The biosolids shall be applied at a rate that is equal to or less than the agronomic rate (typically based on nitrogen).

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The following site restrictions apply to cropland, if the biosolids meet Class B characteristics and not Class A:

§ Animals cannot graze on site for 30 days after application. § Public access to land with a high potential for public exposure shall be restricted for 1 year after application of the biosolids. § Public access to land with a low potential for public exposure shall be restricted for 30 days after application of the biosolids. If any crops, including feed crops, are grown on this land, additional site restrictions will apply. The biosolids must meet at least Class B requirements if it is to be land applied to any type of cropland.

A potential consideration that may be associated with the land application of biosolids outside the current CD boundary is the permitting implications associated with the existing biosolids and wastewater permits. If biosolids are applied to areas outside of the current CD, amendments to both permits and/or the CD would be required.

In addition, climatic conditions will restrict sludge application for time periods throughout the year. Therefore, to account for the application restrictions due to weather and crop schedules, the sludge can realistically only be applied for eight months of the year in most typical years. Considering the climate and crop restrictions, it would seem best to assume that primarily harvested solids (from FSBs) could be used for off-site land application. Work of other agencies has shown this product has improved dewatering characteristics and is more desirable to users and the public (less odor than sludge immediately dewatered from the digesters).

Truck transport is widely used for transporting both liquid and dewatered sludges because it offers the flexibility to readily change terminal points and route-of-haul at low cost and investment in terminal facilities can be minimal. Also, many truck configurations are available, ranging from standard tank and dump bodies to specialized equipment for hauling and spreading liquid and dewatered sludges.

Off-Site Land Application – Air Dried Dewatering using belt filter presses prior to air drying is a common approach and may be cost- effective in terms of minimizing the air drying area required. Should this become an option in the future, air drying of harvested sludge from FSBs is preferred to drying digested sludge (i.e., sludge directly from the digesters) since harvested sludge is much more stable material and will therefore produce far less odors during air drying operations.

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Air drying needs to be conducted on paved areas or drying beds, usually asphalt beds, so that mechanical equipment can be used to mix and turn the material to promote faster and more complete drying. Paved areas are sloped to promote removal of precipitation, however, runoff must be retained on-site for processing, evaporation, or for disposal by other means.

Air dried sludge can vary widely in solids content. Material as low or lower than as 40 percent solids has been successfully reused in off-site land application programs. Typically, sludge is air dried to about the 60-percent solids range in climates similar to that in the Colorado Springs area, especially in the warmer months. Reducing moisture content is extremely helpful in reducing transport costs and in providing product storage in dried material stockpiles.

With this option, off-site agricultural lands need to be identified and permitted, as necessary, to accept Class B sludge. Monitoring and record keeping requirements need to be followed carefully to satisfy all rules. Land application of air dried Class B sludge is a common method of beneficial use, especially in the more arid climates of the Western US where space is generally more available for air drying operations.

Off-Site Landfill Cover or Land or Mine Reclamation Free liquids are prohibited at most landfills, therefore transport of sludge that has been stabilized and dewatered/dried to a landfill for use as daily cover on a regular basis could be an option. In addition, dewatered/dried product could be an option for use in land reclamation opportunities.

Sludge storage would not be required with this option because a landfill operation is not usually interrupted by weather. However, for operation purposes, a small sludge storage or staging area may be necessary at the landfill or land reclamation site for sludge handling and mixing.

Beneficial Use – Class A A sludge that meets Class A pathogen reduction, meets vector attraction reduction requirements, and contains low metals concentrations within the “Alternate Pollutant Concentrations” is called “Exceptional Quality” (EQ) sludge and can be employed in a wide range of uses. Because an EQ sludge meets a high level of quality, its uses are essentially unrestricted. This means that with very little monitoring and record keeping requirements, an EQ sludge can be used in home gardens, on golf courses and parks, in nurseries, in cemeteries, and along highway medians and rights-of-way. If a sludge product meets Class A pathogen requirements but has metals concentrations above the “Alternate Pollutant Concentrations,” then some additional management practices beyond those required for EQ sludge would be required.

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It is desirable to have Class A or EQ options which would produce marketable material from the sludge and could be used by the community or public agencies as a soil amendment. If a Class A option that handles only a portion of total sludge production is pursued in the future, Colorado Springs Utilities would gain from the experience, which would make any transition to full production of Class A material easier.

The market for Class A sludge products must be thoroughly investigated prior to embarking on a capital program to construct permanent facilities to produce a this material. Other products that will compete with Class A sludge in the soil conditioner market include animal manure, peat moss, commercial fertilizer, and topsoil. While certain management activities, such as monitoring and record keeping, will be reduced with an EQ sludge, other management practices such as marketing and distribution of the sludge will increase. The advantages and disadvantages must be carefully considered. Liability issues must be addressed when considering offering a product to the public.

The following is the list of potential Clear Spring Ranch Class A beneficial use options discussed throughout the Masterplanning project. The following options are described in the paragraphs below.

§ Heat dried product § Composted product § Land application – cake product § Land application – air-dried product § Landfill cover or land reclamation – cake § Landfill cover or land reclamation – air-dried

Heat Dried Product Heat drying of digested, dewatered sludge has several advantages: it stabilizes sludge and reduces sludge volume by drying it to less than 10 percent moisture content; it does not destroy volatile solids in the sludge; pathogens in the sludge are killed at the high temperatures used (175 degrees F and higher); and lack of moisture prevents renewed biological activity. One consideration is that heat-dried sludge must be kept dry until final disposal because a moisture content above 10 to 12 percent will allow resumption of biological decomposition of organic material. Heat drying kills all pathogens because of the high temperatures; therefore it meets Class A pathogen reduction requirements.

Wastewater sludge heat drying may be accomplished by direct or indirect means. Direct heat drying equipment introduces dewatered sludge into a stream of hot gases where water is removed by evaporation. An advantage of direct sludge heat drying systems is that they can be started quickly and operated intermittently. However, complex equipment is required to remove dust emissions and odors from the gas prior to discharge to the atmosphere. In comparison, indirect heat dryers eliminate the large volume of dirty and odorous gas associated with direct heat drying of sludge.

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Indirect dryers use a hot surface to transfer heat into dewatered sludge and evaporate the remaining moisture. The gas stream from the dryer is small and requires only the volume of air necessary to remove the evaporated water.

Heat dried sludge makes an excellent soil conditioner and a good fertilizer, though its benefits are incomplete unless it is fortified with certain nutrients. Heat dried, digested sludge contains less nitrogen than most fertilizers and is more valuable for its soil conditioning and building qualities than for its fertilizer content.

Marketing/Distribution. Marketing and distribution of heat dried sludge products are normally handled through contractors or even fertilizer brokers, although occasionally a wastewater agency will handle these activities internally. Depending on the characteristics and quality of the product, particle sizes (pellets or granules), nutrient content, and other factors, the product may be blended with inorganic fertilizer materials in dry bulk blending operations to produce specific fertilizer blends for uses in the region. The value of the material makes more wide-spread use possible, often allowing the products to be transported hundreds of miles. Shipment is commonly by truck, or by rail when larger quantities with more distant use sites are involved.

Composted Product Composting converts sewage sludge and other solid wastes into products that can be distributed to the public for a variety of beneficial uses. It is proposed in the federal sludge regulations as an accepted technology for achieving the Class A pathogen reduction. Compost bulking agents can dilute pollutants in the sludge or increase pollutant concentrations, depending on the characteristics of the bulking agents.

The three basic sludge composting methods are: (1) windrow, (2) static aerated pile, and (3) within- vessel. Windrow composting is the simplest method, relying on frequent mechanical mixing to maintain aerobic conditions within the compost mixture. However, to meet Class A pathogen levels, the sludge within the composting process must be kept at temperatures above 55 degrees C for at least 3 days. Meeting the higher temperature requirements at all locations within the windrow composting process can be very difficult, especially in colder climates. For this reason, Class A composting processes for Colorado Springs Utilities are limited to static pile and in-vessel composting processes.

The static aerated pile requires less mixing than windrow, but relies on compressors, air distribution piping, and continuous temperature monitoring to achieve reliable process control. Both methods require relatively large land areas for mixing, stockpiling, and composting. Also, because of their potential to produce odors, both systems may require large buffer zones. In comparison to windrow and static pile, within-vessel composting has high capital costs but lower operating costs, requires substantially less land, and more easily accommodates odor control technology. Using either the within-vessel composting method or the static aerated pile composting method, the temperature of the biosolids is maintained at 55 degrees Celsius or higher for 3 days.

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Problems with large-scale composting operations have been experienced by many municipalities. Specifically, odor problems and the lack of adequate markets for large compost volumes are well documented. Odor problems and land area requirements associated with static pile and windrow composting have encouraged the use of within-vessel composting. And although within-vessel method does not reduce composting odors, it is easier to treat the odors because there is a smaller volume of air to treat. Many static pile and windrow composting operations are now being enclosed in large, warehouse-type structures to control and treat odors and to protect the operation from inclement weather.

Colorado Springs Utilities has previously researched and evaluated biosolids composting at the facility and determined it not feasible at this time. Beginning in May 1997, a Biosolids Composting Pilot Project was completed by The Scotts Company. The purpose of the study was to evaluate different composting techniques and determine the most feasible technique for Clear Spring Ranch. A 5- to 10- acre parcel was designated as the “pilot project area”, with an active composting area of 2 acres. Ten test windrows were in place. During the project, an operational plan was generated, and metals data, microbial parameters, and dry weight were recorded. In October 1998, this project was determined not feasible and not expanded to full scale.

In April 1999, Colorado Springs Utilities investigated composting options again. Options included off site land application, on-site land application, and on-site composting. In January 2000, Colorado Springs Utilities determined that these options were not favorable, but that they would continue to re-evaluate the potential to compost in the future. The basis for not selecting composting in the past was based on costs and impact on wastewater rates, lack of data from previous studies needed for decision making, the need for future evaluation of other alternatives, and regulatory concerns.

Land Application Using Cake Product Production of Class A dewatered sludge cake provides a wide potential market for sludge use. Agricultural land application would be the largest potential use of this material, since use on golf courses or parks would be aesthetically unacceptable.

There are several possible ways of producing Class A dewatered cake. Some of the more feasible methods are listed here:

1. Use thermophilic anaerobic digestion in batch arrangements to meet EPA’s time/temperature criteria for Class A sludge.

2. Use pre-digestion pasteurization technology to meet EPA’s time/temperature requirements.

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3. Use FSBs in storage mode for about 1.5 years of “pure storage” to produce pathogen- free sludge. The specific time requirement is subject to refinement based on various research work, since this is not an approved EPA Class A process. Sampling of final product to prove Class A pathogen densities would be required with this approach.

4. Use certain dewatering methods such as vacuum and high temperature pressure filters to meet time/temperature requirements.

Further assessment of such treatment options will be described in Chapter 6. Creating Class A solids through some combination of digestion and FSB operating methods may be relatively cost- effective at the SHDF. A major advantage of using FSBs allows most of the Class A cake product to be produced during the warm weather months by dredging FSBs in concert with dewatering.

While using Class A or EQ cake products in agricultural land application will entail relatively little regulatory oversight, the products would still have the appearance of sludge material. If the Class A technology used does not comply with EPA’s time/temperature requirements, sampling of the final product in batches to prove that it meets EPA’s Class A pathogen density limits would be required.

Land Application Using Air Dried Product Air drying can achieve Class A pathogen reduction requirements, but actual pathogen reduction needs to be demonstrated for each site.

Wet sludge slurries are usually applied to a depth of approximately 9 inches onto paved beds. The sludge is left to drain and dry by evaporation. Mechanical mixing or turning is frequently added. The effectiveness of this process depends on the local climate. Drying will occur faster in warm, dry weather and therefore, assumed only seasonably feasible.

Since air drying of digested, dewatered cake has not always produced Class A sludge, additional treatment will be necessary. Such Class A treatment can be provided by higher-temperature digestion (thermophilic) or increased storage time in FSBs, or perhaps some combination of these processes. If the Class A technology used does not comply with EPA’s time/temperature requirements, sampling of the final product in batches to prove that it meets EPA’s Class A pathogen density limits would be required.

Landfill Cover or Land Reclamation – Cake Product This option consists of transporting stabilized and dewatered sludge to a landfill for use as daily cover or to land reclamation sites on a regular basis. However, Class A sludge requires further treatment or processes to further reduce pathogens to achieve lower pathogen levels than Class B.

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Landfill Cover or Land Reclamation – Air-Dried This option is similar to the item above, except the Class A air dried sludge is used for landfill cover or at land reclamation sites.

Biosolids Beneficial Use Options In Colorado Biosolids have been recycled in Colorado since the early 1980s, and in other places in the United States since the 1920s. Many Colorado soils lack sufficient organic matter, therefore adding biosolids improves them. Organic matter can provide nutrients necessary for microbial activity in soils, which make nutrients available to plants. Typical Colorado biosolids have a nutrient value of about 6 percent nitrogen, 2 percent phosphorous, and 0.02 percent potassium. The microbial activity also improves structure, creates air spaces in soil, called pores, which increase the soils ability to hold air and water. The addition of organic matter improves both clayey and sandy soils. In soils with high clay content, the increased air and water holding capacity assists in reducing surface runoff and its associated erosion area. In sandy soils, the increased water holding capacity allows more of the nutrients remain in the root zone rather than leaching out of the soil. Increased water infiltration into soils means more water stored for the growing season, an important benefit in our semi-arid climate.

Increased amounts of treated sludge are being applied directly to agricultural land. This promotes sludge decomposition with subsequent benefits to soil and crop production. Land application provides a municipality with a feasible means of managing its sludge; and it provides organic matter to improve soil physical conditions and supplement conventional fertilizers.

Local Beneficial Use Study An example of a regional beneficial use study was obtained from information provided by the Littleton/Englewood (L/E) WWTP. In 1982, the L/E WWTP contracted with the Colorado State University Department of Agronomy to study the benefit and environmental impacts of biosolids application versus the use of nitrogen fertilizer on dryland wheat fields. The soil condition, accumulation of metals, moisture content, and grain quality were measured as part of the study.

The L/E 15-year, on-going study is one of the most in-depth and continuously running studies conducted by any Publicly Owned Treatment Works in the nation. The data collected as a result of this study has been used to assist in the development of federal and local biosolids regulations.

In 2003, L/E and Colorado State University worked together on three biosolids related projects. The project from 1982 will continue, as will a similar study in Kiowa, though the focus will be more on how biosolids impact ground water. The third project, slated to begin by the end of this year, will look at biosolids application and progressive farming methods, including crop rotation schemes.

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L/E reports that Colorado is above the national average in its use of recycled biosolids and 85 percent of Colorado’s biosolids are used in either agricultural uses (60 percent), reclamation (forests, golf courses, revegetation of mining areas, 20 percent), or sold to nurseries and private citizens (5 percent). Only 15 percent is sent to landfills as opposed to the national average of 50 percent.

Local Examples of Beneficial Biosolids Application Within Colorado, 123 facilities participate in the beneficial use of biosolids, which includes land application, composting, and sale to other parties. Of the 91,688 dry metric tons of biosolids land applied in 2002, 12,861 dry metric tons were generated out-of-state and imported for use in Colorado (CDPHE BDMS database). The continued use of and demand for recycled biosolids product demonstrates a highly viable system in Colorado.

Metro Wastewater Reclamation District of Denver (District) is a municipality participating in biosolids recycling. The District began biosolids composting in 1986. Primary and secondary solids are stabilized in anaerobic digesters. The biosolids are dewatered using large centrifuges into a semi- solid “cake.” The approximately 74 dry tons of the resulting biosolids that are produced daily are used as soil amendments to enrich agricultural lands. The biosolids are applied to 50,000 acres of District-owned land near Deer Trail, Colorado, and on privately owned land in northeastern Colorado. Ninety-five percent of the District’s biosolids are applied to agricultural land in cake form. Biosolids cake is also used to make compost, a peat moss-like soil conditioner. The District has marketed both products as METROGROTM Cake and Compost. US EPA and CDPHE regulations govern application to District and privately owned agricultural land. These products are used as fertilizers and as soil conditioners, with many of the benefits described above.

Parker Ag Services coordinates the importing of biosolids from other states into Prowers County, Colorado. New York City produces approximately 1,200 dry tons of biosolids daily from its fourteen water pollution control plants. In 1990, a land application program began in Prowers County that utilizes cake biosolids from New York City. This program is ongoing and currently has a contract through 2012. Due to realized benefits of land application, strong relationships with farms, regulators, and elected officials, and improvements in New York City’s pretreatment program, the program has proved successful and has expanded over the years and still continues today. Currently, approximately 350 wet tons/day was imported from both New York City and Boston. In 2002, over 30,000 dry tons were imported. The biosolids included dewatered Class B cake biosolids from New York City and Class A pelletized biosolids from the New England Fertilizer Company in Boston. The total acreage of permitted application sites is approximately 40,000 acres, and the local health department is involved in monitoring and oversight of application.

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Biosolids Compost Production and Use In 1996, nineteen state DOTs had specifications for compost, and thirty-four DOTs reported experimental or routine use of compost on roadsides. Compost was used as a soil amendment, a component in manufactured topsoil, a mulch or topdressing, for erosion control, in hydroseeding, wetlands mitigation, filtration berms, and bioremediation.

Marketability of Biosolids Products The condition of the recycled biosolids market is affected by environmental, political, economic and other factors. Respectively, these factors support the need for biosolids recycling, encourage heightened standards to ensure public health and safety, and increase the cost-effectiveness of undertaking certain forms of biosolids recycling.

Air dried products. Agricultural land application could involve hauling air-dried biosolids to local farms and apply them to agricultural fields at agronomic rates. Hauling and application contractors are available and bidding and contract agreements can be prepared to advertise for these services. Using air-dried biosolids is common practice in arid portions of the Western United States. Having too dry a product (<60 to 70 percent solids) has led to dust problems during spreading at some sites, and restrictions in applying during high windspeeds may be necessary.

Heat dry product for fuel value. Dewatered raw sludge could be a likely feedstock to the potential recirculating fluidized bed boiler (RFBB) to minimize the quantity of water being sent to the unit, yet retain the fuel value of raw sludge, which is considerable. However, there are relatively few examples of this approach for wastewater sludge management. The reasons for limited use of this approach include the following:

§ Few POTWs have relationships with power plants to forge the necessary long-term arrangements for this approach. § Sludge would normally be a small percentage of feedstock for a power plant and would typically have different characteristics than other fuels, so that special feeding/handling and operating conditions are needed for the sludge material. § There may be pollutants in the sludge that affect the air emissions or air permitting limitations of the power plant.

There are reportedly a few examples in Germany of using dewatered (or heat dried) sludge as feed for power plants (usually mixed with coal). The reasons it may be more attractive in Germany are that biosolids use in land application is very restrictive there, and costs for sludge disposal in landfills or similar places is much higher in Europe than in the United States.

Compost products. As indicated in the above examples, many municipalities are successfully utilizing biosolids to create and market recycled compost products.

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Heat dried sludge for fertilizer/amendments. More than 50 municipalities in North America have implemented sludge heat drying. Major, marketing strategy enhancing, advantages of dried biosolids are that the heat required to dry the material essentially ensures that pathogenic organisms are destroyed so that issues of public health and safety can be more readily addressed; the nutrients in the biosolids are not diluted by bulking agents, thus maintaining maximum nutrient content which can appeal to farmers and other users; and the nutrient value is sufficient to allow transporting the material hundreds of miles. A major disadvantage of dried biosolids is that they can be considered by municipal authorities to have too high a risk because they are combustible. This presents a marketing challenge. In examining the advantages and disadvantages of heat-dried biosolids recycling, major marketing factors include the following: nutrient content; moisture content; whether the product is free from pathogens; whether the particle size is suitable for the end user; the density and shape of particles to minimize segregation and ease spreading and handling; durability; minimizing dust; ability to dissolve in soil; odor; and the presence of foreign matter. Marketing, distribution, and land application of dried product can be handled in many different ways, but are commonly handled through contractors and fertilizer brokers.

Public Acceptance and Concerns Numerous municipalities are utilizing biosolids recycling and are successfully marketing the products. A critical key to the success of a biosolids land application program is an informed and educated community. In the case of importing biosolids from New York City for land application in Prowers County, described above, the program was temporarily halted in 1993 when ownership of the program shifted and public education and outreach efforts were neglected and consequently, newly elected officials banned the land application program. However, the effects of initial educational efforts and realized benefits persisted and the program was reinstated as a result of requests made by farmers who experienced benefits from the program. Another critical component to gaining public support and confidence is the involvement of local regulators and health departments in providing oversight.

In some areas of the country, particularly California, Virginia, and New England, many counties have established restrictive ordinances in the last five years aimed at eliminating or restricting biosolids use in land application programs. Some ordinances allow only Class A or EQ material to be used, or make site permitting so difficult that there is limited interest in conducting land application. Most of these ordinances are driven by public fears of possible health impacts associated with land spreading.

In July 2002, the National Academy of Sciences released a report, “Biosolids Applied to Land: Advancing Standards and Practices”, which stated that existing regulations, in particular Part 503, were protecting public health. In addition, the report also stated that additional scientific research on the subject was needed to disperse public fears, and that some of this work was already being carried out. The Biosolids Committee of the RMWEA has endorsed the safety and benefits of biosolids recycling.

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Chapter 6. Process, Treatment, and Disposal Options

Overview The objective of this chapter is to identify process, treatment, and disposal options for the SHDF by maximizing the use of existing facilities. This chapter presents components of the existing system as well as investigates new technologies, describes the initial beneficial use and treatment process screening, and describes the selected alternatives that will be evaluated in Chapter 7.

The following sections evaluate potential improvements or new technologies that may be recommended at the SHDF. Each of these sections describe in detail the process and its feasibility at the SHDF.

§ Pumping and Thickening § Digestion options and enhancements and struvite control options § FSB options and improvements § DLD options and improvements § Dewatering § Heat drying § Air drying § Use of sludge as fuel to a recirculating fluidized bed boiler § Offsite beneficial use and disposal methods

Pumping and Thickening Raw Sludge This section evaluates the pumping of raw sludge in the Sludge Main and discusses potential sludge thickening systems.

Pumping Sludge to the SHDF Table 6-1 shows recent history and near-term projections for the Sludge Main to the SHDF, assuming that thickened sludge at about 3.1 percent solids is pumped. Prior to the new 14-inch diameter pipe coming into service, the transit time in the Sludge Main was about 30 hours, with an average velocity of only 0.8 ft/second. This is a longer transit time than any known raw sludge pipeline in North America. Based on sludge characteristics at the pipe discharge, it is obvious that fermentation and acid-phase digestion is occurring within the pipe, with discharge volatile fatty acids (VFAs) of about 3,000 mg/L, low pH (average about 6.0), and some solubilization of volatile solids in transit. There was reported to be relatively limited gas production in the Sludge Main prior to the first 14-inch sections coming on-line in 1999/2000.

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Grease/scum is collected separately at Las Vegas Street WWTP from the clarifiers and trucked to the SHDF every 10 days or so, where it is introduced into the digesters. Therefore, the separated grease/scum stream is not included in the sludge flow that is pumped through the Sludge Main, however, primary sludge contains much greasy and grease-like material. The pumped sludge averages about half primary and half waste activated sludge on a mass basis.

With now about two-thirds of the Sludge Main length having 14-inch diameter pipe, average transit time has increased dramatically to about 2 days and velocity in the 14-inch reaches is only 0.5 ft/second. This low velocity may cause concerns for accumulations of grit and debris in the 14-inch pipe, and the extreme transit time raises questions about increasing gas production in the pipe. Sludge characteristics at the discharge show some increase in VFAs and further decrease in pH, indicating even greater degree of acidification, fermentation, and acid phase digestion.

Grit/debris accumulation may not be a major factor when pumping mixed raw sludge at these solids contents (i.e., 2 to 3+ percent solids) since this situation involves semi-plastic, non-Newtonian flow which would entrain the grit/debris within the slurry mass. This type of thick sludge flow is much different from low-solids content flowstreams (liquid-dominated, Newtonian) where grit must be dragged along the bottom of a sewer or forcemain to avoid buildup.

Table 6-1. Sludge Main and Solids Characteristics Parameter 1998 2002/2003 Conditions Estimated 2005 Conditions Sludge Main: Length 17.6 miles 17.6 miles 17.6 miles Pipe Diameter All 10 inch 10 inch ~6 miles All 14 inch 14 inch ~12 miles Pipe Volume 379,000 670,000 742,000 (gal) Gas Relief Valves Automatic, but they have not Manual on 14 inch Manual on 14 inch worked in auto. Pump Conditions: Typical Pressure at 150 to 250 psi 150 to 300 psi 150 to 300 psi Pumps Flowrate (Ave.) 290,000 330,000 350,000 gal/day Solids Content (%) 2.9 3.1 3.1 Time in Pipe Transit 31 47 51 (hours) Velocity 0.82 (10 inch) 0.93 (10 inch) 0.50 (14 inch) (ft/sec-Ave) 0.48(14 inch) Sludge Temp. Range 12 to 22 °C 12 to 22 °C 12 to 22 °C (Seasonal)

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Parameter 1998 2002/2003 Conditions Estimated 2005 Conditions Sludge Discharge Characteristics: Outlet pH ~6.0 ~5.6 ~5.6 Outlet VFAs (mg/L) ~3,100 ~3,500 ~3,700 Outlet Alkalinity ~1,800 ~1,800 ~1,900 (mg/L) VSS changes inlet to Reduction in VSS- difficult to Same Same outlet quantify. Gas Production in Reported to be little gas Much greater gas production Increasing gas production Pipeline production. causing operational problems. with longer transit times – more problems expected. Grit deposition and Velocity less than 1 ft/sec. Velocity is extremely low Possible increasing potential debris accumulation There was a major several- (<< 1.0 ft/sec). Possibly of pipeline plugging. in Sludge Main: day grit plugging event in 10- increasing potential of inch pipes in 1999, caused by pipeline plugging. peak storm grit load in primary sludge.

Struvite/Scales in Struvite scales in DS and Large piles of scale material If scales are PO4 induced and digesters Recirc. piping at digesters and within digester taken out of long pipeline transit time struvite buildup on FSB service in May 2003. Very causes more PO4 release, mixer blades. different scale situation from then greater scale piles are anything seen previously at predicted with longer transit SHDF. times.

Significant gas production is now occurring within the Sludge Main. Gas is discharged out the end of the pipeline regularly, sometimes occurring in long slugs of mostly gas, other times occurring as joint gas/slurry flow. Gas is being trapped at various high-point locations and reaches in the pipe, and builds up to levels that cause operational problems. Occasionally, Colorado Springs Utilities staff need to bleed off gas from certain gas relief valves, however, this has not caused odor problems to date since there are few neighbors along the Sludge Main right-of-way. The gas is no doubt mostly carbon dioxide, but would probably contain some hydrogen, nitrogen, and methane, in addition to hydrogen sulfide and many other highly odorous compounds.

Struvite scale problems at the SHDF are discussed later in this chapter. As discussed there, the longer pipeline transit times in the last 2+ years are likely to be a factor in recent extraordinary scale piles found in a digester cleanout in May 2003. The longer pipeline transit time in these last 2+ years has provided greater acidic conditions for more time. This situation is probably responsible for increased phosphate solubilization within the sludge during pipeline travel, thus causing a different type of scale-production situation within the digesters. One sludge sample tested in October 2001 showed orthophosphate-P concentrations of about 200 mg/L in the sludge sent to the digesters (Preliminary Report Clear Spring Ranch Excess Water Study, 2002). This would indicate very strong phosphate solubilization during Sludge Main transit. Since PO4 is usually a limiting factor in struvite production, high levels in the liquid stream will cause excessive struvite

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production. Preliminary testing confirmed that the material forming in the digesters was struvite. Further testing will confirm the causes.

Table 6-1 indicates expected conditions in 2005 with the full-length 14-inch Sludge Main in service, and assuming that the feedrate to the pipeline is 350,000 gal/day. Under these conditions, average transit time rises to 51 hours and additional gas production is likely.

Other Long Sludge Pipeline Situations Table 6-2 lists several other long raw sludge pipelines, and key operating parameters associated with each. From this table and information in the literature, the following seems apparent:

§ The transit time within the Colorado Springs Utilities Sludge Main (currently about 48 hours) is much longer than any known sludge pipeline. Typically, agencies limit sludge pipeline transit times to about 10 to 12 hours due to extreme septicity and difficulty in handling the sludge discharged from pipelines with longer transit times. § Sludge pipeline velocities are almost always at least 1.5 to 2.0 ft/sec. The current Colorado Springs Utilities Sludge Main velocity (0.5 ft/sec) is significantly less than any other known sludge pipeline. However, because of the high solids content at Colorado Springs Utilities (3 percent solids), the more typical velocity criteria for wastewater pipelines do not apply. § Colorado Springs Utilities is the only known agency which pumps sludge in a long- distance pipeline (i.e., many miles) with no downstream thickening process prior to digestion. All other agencies, given similar situations, are pumping relatively thinner sludge (typically 0.5 to 1.5 percent solids) and are performing thickening or other processing on the sludge after its discharge from the pipe. § Colorado Springs Utilities is unique in that there is no WWTP at the downstream end of the pipeline. Other known situations pump sludge between two WWTPs so that there are options in processing the sludge and various recycle streams (i.e., from thickening, etc.) at the downstream end. The situation at San Diego is somewhat similar to Colorado Springs Utilities since the Metro Biosolids Center (the downstream location at San Diego) is a sludge-only processing plant; however, thickening, dewatering and other waste or recycle flows generated at MBC are discharged to local sewers which lead to a large downstream WWTP – the Pt. Loma plant in San Diego.

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Table 6-2. Long Raw Sludge Pipelines and Operating Conditions Percent Solids Transit Agency/Location Length-Diameter Comments Time/Velocity Northeast Ohio Sewer 13.2 miles At startup~3 percent Efforts to thicken at District - Cleveland Original=12 inch solids. Reduced to 1% downstream end were not Easterly to Southerly Newer Pipe= 16 inch after some years. Now < successful- extremely odorous Plants P/WAS combined 1% solids and 4 to 8 sludge. For 20+ years, they have hours in transit. Velocity pumped sludge into headworks well over 2 fps now. at Southerly Plant. Indianapolis, Indiana - 7.5 miles 1 to 1.5% solids. Velocity Thickening downstream Southport to Belmont twin 14 inch reported about 2 fps. reported to be difficult due to Plant P/WAS combined About 4 to 6 hours septicity of solids. transit time. San Diego, California - ~6 miles ~0.5% solids Thicken downstream with North City plant to 16-inch pipe 4 to 6 hour transit. centrifuges to 5.5% solids for Metro Biosolids Center P/WAS combined Velocity ~1.5 fps. pH~ digester feed. Good capture. (MBC) 6.0 to 6.7 when arrives at Polymer dose 3 to 4 pounds per MBC. dry ton. Centrate to sewer to Pt. Loma Plant. FeCl3 at 80 to 160 mg/L added at sludge pump station for sulfide control in force main. Chicago Northside to 18 miles ~1% solids Thicken downstream with Stickney Plant 14 inch pipe 8 to 10 hour transit gravity thickeners but this is P/WAS combined Velocity 2.5 fps difficult and extremely odorous. Poor performance.

Sludge Velocity and Gas Production in the Sludge Main Methods to increase sludge velocity and limit gas production in the Colorado Springs Utilities Sludge Main are identified here.

1. Pump Thinner Sludge. Pumping thinner sludge increases velocity and reduces transit time in the pipeline, but has major consequences at the SHDF. Any increased flow currently means that additional digesters would need to be operated and there is barely enough digester gas generated in the winter to heat existing flowrates for mesophilic digestion. In warmer months, pumping somewhat thinner sludge is possible. Pumping thinner sludge would also help minimize struvite problems. Pumping thinner sludge and conducting thickening downstream at the SHDF is a further option that is discussed below.

2. Add Chemicals. Various chemicals can be added to the sludge flow to minimize biological activity in the pipeline and perhaps keep pH up. This would include caustic or lime to raise the pH, chlorine (sodium hypochlorite) or hydrogen peroxide to prevent/minimize biological action for a certain period of time, and iron chloride to slow down reactions and tie up sulfide. However, this approach would do nothing to increase sludge velocity. And, such an approach is likely to be very costly in terms of chemical usage.

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3. Insert a Pipe Within Existing Pipe(s). A smaller pipe (such as 8 inch or 10 inch) would increase the velocity significantly. Such smaller diameter pipe might be inserted within the 14-inch pipe or within one of the older 10-inch pipes. However, an 8-inch pipe would provide inadequate capacity for the future, so this is not attractive. Feasibility of retrofitting a 10-inch pipe within the 14-inch pipe or reconstructing one of the older 10-inch pipes would need more detailed investigation, and at this time such options are not pursued.

Pumping Thinner Sludge to the SHDF The situation for a single-pipe system is different than when Colorado Springs Utilities had a 2-pipe system. The former twin-pipe arrangement had low velocity (about 1 ft/sec or slightly less), but this had been judged acceptable since there was a backup pipe available in case an operating problem or accident occurred. With single-pipe operation, pipeline reliability needs to be maintained at a higher level, to insure less risk of being out of service. Reliability factors include potential plugging, gas production/gas binding, potential damage from various types of accidents, long-term pipe corrosion, and structural failure. Now that the 14-inch Sludge Main is largely built and operating, the primary variable that can be controlled is pumping rate and resulting sludge velocity. Perhaps more detailed reliability review is warranted on single-pipe operation, however, based on the very low velocity and high transit times now occurring, gas production is judged to be a significant risk and reduced transit times are recommended.

Table 6-3 provides alternative pumping/velocity conditions and indicates a recommended velocity range of 1.0 to 1.5 ft/sec. Obviously, as velocity rises, flowrate rises, and sludge with reduced solids content is pumped. The major disadvantage of higher velocity is that more water must be handled at the SHDF. This extra water would most likely be generated as recycle flow from a sludge thickening process.

Pumping higher flowrates also affects the pumps at the BSPS. The three Abel high-head pumps are designed for pumping relatively thick solids (such as 2.5 to 3.5 percent solids) and relatively low flowrates (several hundred thousand gallons per day). Peak capacity is estimated to be about 770,000 gallons/day with all 3 pumps operating. Additional or different pumps would probably be necessary for pumping up to 1.5+ mgd peak flowrates of thinner solids (such as 1.0 percent solids). It would appear that pumping up to 700,000 gallons/day could be accommodated with existing BSPS pumping equipment, although the solids content would need to drop to about 1.5 percent to achieve this increased flowrate.

There is a thickened sludge storage tank located adjacent to the BSPS at the Las Vegas Street WWTP. This tank is used to provide up to about 3 to 4 days of thickened sludge (at about 3 percent solids) emergency storage in the event the pipeline or pump station cannot be operated. Even with modified sludge pumping operation, this emergency sludge storage tank system should be retained.

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Table 6-3. Alternative Pumping Conditions in the 14-inch Sludge Main Parameter: 0.5 fps 1.0 fps 1.5 fps 2.0 fps 2.5 fps 3.0 fps Ave. Transit time 52 26 17 13 10 8.6 in Pipe (hours) Flowrate Required 0.35 0.70 1.05 1.40 1.75 2.10 (mgd) Solids Content in Pumped Flow: 2005 3.1% 1.55% 1.03% 0.78% 0.62% 0.52% 2025 (City) 4.1% (not feasible)ª 2.0% 1.35% 1.07% 0.81% 0.68%

2025(County) 5.9% (not feasible)ª 3.0 2.0% 1.5% 1.2% 1.0%

Suggested Flow X¹ X² Regimes in Future ª This situation is infeasible because the sludge is too thick and headloss is expected to be too great for the current pumps to handle. ¹ Current BSPS should be able to handle this pumping option. ² Current BSPS probably not able to handle this pumping option.

Modified Thickening at Las Vegas Street WWTP Modifying the sludge thickening system at Las Vegas Street WWTP to create even thicker solids is not deemed feasible since this would worsen the sludge velocity problem in the Sludge Main. To pump thinner solids in the Main, the operation of the sludge thickening system would need to be modified to allow only partial thickening, where only a small portion of sludge is actually thickened and then blended with unthickened sludge.

Sludge Thickening at the SHDF Providing a thicker feed to the digestion process at the SHDF is desirable for several reasons:

1. Reduce the number of digesters that need to be operated in the near-term. 2. Cut sludge heating requirements as a result of reduced digester feedrates 3. Delay the time that additional digesters would need to be constructed.

There are several potential types of thickening processes that could be used – such as gravity belt thickeners, centrifuges, dissolved air flotation thickeners, drum thickeners, etc. However, with the characteristics of the solids arriving at the SHDF (fermented, low pH, and extremely odorous) the thickening process would need to be fully contained. Therefore, we believe centrifuges are the appropriate technology to consider for this application. Evidently, gravity belt thickeners (GBTs) have been previously discussed for possible use in raw sludge thickening at the SHDF. However, the severe odor situation would require that the units be completely contained for operators to work near them, thus making operation and maintenance difficult. Also, for unattended or minimal- attended night-time operation, GBTs may not be acceptable.

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Table 6-4 shows the conditions associated with centrifuge thickening at the SHDF assuming 1.0 ft/sec velocity in the sludge pipeline (0.70 mgd average Sludge Main flowrate). It is assumed that thickening of this sludge to 5.5 percent solids is possible, with 95 percent capture at a reasonable polymer dose (these assumptions would need verification in pilot testing work if this option is pursued). Based on these assumptions, the centrate characteristics are shown in Table 6-4. The thickening option would need to be conducted 24 hours per day and be a very reliable operation because digesters are being fed the thickened material. Unattended thickening operation during weekend and nighttime shifts at the SHDF is probably possible, but this would need further evaluation and clarification. Thickening only during daytime shifts, with thickened sludge storage and continued digester feeding at night, complicates the situation and is not desirable.

Table 6-4. Raw Sludge Thickening at the SHDF (assuming 700,000 gal/day sludge flowrate) 2005 2025 2025 Parameter Conditions City-only County Ave. Velocity on 14-inch 1.0 fps 1.0 fps 1.0 fps Sludge Main Raw Sludge Flowrate 0.7 mgd 0.7 mgd 0.7 mgd Solids Content 1.55% 2.0% 3.0% Centrifuge Thickening System: Thickened Solids Capture Assume 5.5% solids Same as prior column. Same as prior column. Polymer Dose 95% capture. 4 to 8 lbs/dry ton. No. of Machines (24/7 2@ 250 gpm each 2@ 250 gpm each 2@ 250 gpm each operation) +2 spare +2 spare +2 spare Centrate: Flowrate Ave. 0.51 mgd 0.45 mgd 0.34 mgd Sus. Solids (mg/L) ~800 to 1,500 ~1,200 to 2,000 ~2,500 to 3,500 PH ~6.0 ~6.0 ~6.0 BOD (mg/L) 2,000 to 3,000 2,000 to 3,000 2,000 to 3,000 VFAs (mg/L) ~2,500 ~2,500 ~2,500 Ammonia-N (mg/L) 150 to 300 150 to 300 150 to 300 Ortho-P (mg/L) 50 to 200 50 to 200 50 to 200 Odor - Very High Odor- Note: Centrate characteristics represent best estimates based on current information. Analytical work is needed to confirm future centrate characteristics from thickening.

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Thickening Centrate Handling/Processing The centrate characteristics make it difficult to handle primarily because of the solubilization and acidification that has occurred within the Sludge Main. Discharging the centrate to the open Supernatant Lagoons would be ill-advised due to odor emissions and potential groundwater infiltration. Discharging the centrate to the FSBs may also be unacceptable for odor emission potential as well as the potential for upsetting the biology within the FSBs. However, FSB discharge would be an option that could be tested to determine feasibility. For master planning purposes, we believe assumptions should include treatment of the centrate. Options include:

§ Anaerobic digestion in a covered lagoon configuration. Gas would be collected and probably flared, although if the gas quality was satisfactory the gas could be combined with digester gas and combusted for its energy value. § Upflow Anaerobic Sludge Blanket Reactor. The centrate would be pumped through a packaged, skid mounted system. Process would consistently remove high levels of COD and nitrogen compounds. These systems are widely used in the ethanol production industry, and produce useful amounts of biogas.

The quantity of centrate flow totals between 400 and 600 acre-feet per year assuming a Sludge Main flow of about 0.70 mgd. Following the above anaerobic treatment, estimated centrate characteristics are shown in Table 6-5. Also shown in Table 6-5 are estimated characteristics if this treated centrate is discharged through the FSBs and then becomes FSB supernatant stored in the Supernatant Lagoons. Either stream (treated centrate or FSB supernatant) then needs to be handled in some manner for final treatment or use/disposal.

Table 6-5. Estimated Excess Water Characteristics Treated Centrate FSB Supernatant-Probably Parameter from Sludge Thickening from Supernatant Lagoons Flowrate 0.35 to 0.5 mgd (400 to 600 acre-feet annually) 0.25 to 0.40 mgd (300 to 450 acre-feet annually)a Susp. Solids 200 to 500 mg/L 150 to 300 mg/L BOD 200 to 500 mg/L 200 to 300 mg/L PH ~7.0 ~7.5 Ammonia-N 200 to 400 mg/L 200 to 250 mg/L

PO4-P 50 to 250 mg/L 100 to 200 mg/L TDS 2,000 to 3,000 mg/L 2,000 to 3,000 mg/L a This would be extra FSB Supernatant over and above what is currently produced. Notes: 1. Further testing is required to refine these estimates. 2. Excess water can be taken as treated centrate or FSB Supernatant. So, excess water is one or the other, not both.

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Processing and Final Use/Disposal of Centrate or Excess FSB Supernatant The 1998 CH2M/Hill report titled “Supernatant Management Plan and Zero Discharge Treatment Evaluation – Hanna Ranch Facility” identified and evaluated several options for handling excess water from SHDF operations. Also, a Colorado Springs Utilities staff report in 2002 titled “Preliminary Report – Clear Spring Ranch Excess Water Study” further evaluated such excess water processing options. Several things are now different from what has been evaluated in previous documents, and one of the primary changes is the increase in the quantity of water created by sludge thickening (because of increased flowrates recommended here for the Sludge Main).

Table 6-6 lists the various options identified for handling water from sludge thickening and for FSB supernatant, and presents previous decisions on these options or expected current thinking about the feasibility of these options. As indicated in Table 6-6, probably the most feasible options at this time for handling and processing the excess water are the following:

§ Irrigate at the Clear Spring Ranch site using this water to grow a crop (poplar trees evaluated in 1998, but other crops should be considered). § Reconstruct, as necessary, a pipeline and pump the water to the Las Vegas Street WWTP for processing. § Should the LFWRF be constructed at the Clear Spring Ranch site, the WRF could be designed to accept and treat the excess water.

Table 6-6. Excess Water Handling Options at the Clear Spring Ranch Options Identified for Sludge Thickener Water and Previous Decisions or for FSB Supernatant Expected Current Thinking on Each Option Evaporation in lined lagoons Costly approach- not recommended. Water treatment via Vapor Recompression (VP) system Higher-technology approach, but could be cost-effective. Water treatment and discharge to Fountain Creek Discharge to Fountain Creek is an option with prior treatment. Should the LFWRF be constructed at Clear Spring Ranch, this could be a viable option. Water treatment and aquifer recharge Risks of aquifer impacts and fairly costly. May not be advisable. Water treatment and reuse at R.D. Nixon Power Plant Relatively costly- does not look attractive. Should the LFWRF be constructed at Clear Spring Ranch, this could be a viable option at the Clear Spring Ranch site. Pipe the water back to Las Vegas Street WWTP for Would require rebuilding and operating 17.6-mile pipeline. treatment. May be more attractive now with larger water quantities to handle than previously evaluated. On-site irrigation of poplar trees or other crop. Fairly reasonable cost and environmentally attractive if sufficient area is available at the Clear Spring Ranch site. Gravel Mines/Adjacent Land Would require treated water. Should the LFWRF be constructed at Clear Spring Ranch, this could be a viable option.

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Evapotranspiration of this much water at the Clear Spring Ranch (assuming 20 inches per year net evaporation rate), would require between 250 and 300 acres. There are approximately 1,500 acres due east and southeast of the SHDF (located on both the east and west side of Interstate 25) within the Clear Spring Ranch Property Boundary that possibly could be used for rangeland or crop irrigation. There are irrigation options in addition to the poplar tree concept, which may have limited crop marketability. Other water reclamation options would suffer from the high cost of further effluent treatment.

Sludge Thickening System at the SHDF A thickening system at the SHDF would need to encompass the following elements:

§ Thickened sludge storage/mix tank to handle a few hours (maximum) of sludge flow and provide a consistent feed to the thickening centrifuges - about 150,000 gallon tank. § Four thickening centrifuges, with feed pumps, polymer system, power supply, control systems, etc., all located in a new structure near the current Sludge Main discharge point and adjacent to the digesters. § Thickened sludge pumping facilities to feed 6+ percent solids to all digesters (normally estimated to be 5.5 percent solids, but capability should exist to pump at least 6 to 6.5 percent solids). § Centrate treatment system – assume Upflow Anaerobic Sludge Blanket Reactor at this time. § Treated centrate or FSB supernatant piping and handling facilities to pump and spread this water for irrigation on about 300 acres of land at Clear Spring Ranch, or pipe the excess water back to the Las Vegas Street WWTP.

Recuperative Thickening at the Digestion Facilities Another method of thickening can be employed within the sludge digestion system at the SHDF. This approach removes liquid from the digesters, but retains the solids for longer solids retention times (SRT). Some additional volatile solids reduction can occur with this approach. Figure 6-1 shows a schematic diagram of this approach.

Thickening equipment used in recuperative thickening can include centrifuges, gravity belt thickeners (GBTs), or dissolved air flotation thickeners (DAFTs). Polymer dose is often significant, however. An advantage of this type of thickening is that the filtrate/centrate can be discharged to the FSBs without further treatment. Also, recuperative thickening would not need to be conducted on a continuous 24/7 basis, but could be operated during hours that the SHDF is normally staffed.

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Figure 6-1. Recuperative Thickening

A major disadvantage of recuperative thickening is that it does not reduce the heating requirements of large digestion flowrates, assuming continued feeding of digesters at about three percent solids. Construction costs for recuperative thickening would be almost as high as for raw sludge thickening described above, and polymer usage and costs for recuperative thickening have proven to be relatively high at other locations. The facilities that are using recuperative thickening are usually accommodating short-term needs while additional digestion tankage is being built, or because there is an operating problem of some kind. On balance, recuperative thickening does not provide sufficient advantages for its costs.

Followup Needs

§ Continue to conduct scientific and engineering work (including analytical work) on the struvite/scale production and control issue to confirm the impact of the Sludge Main operation on scale production in digesters. § Conduct analytical work on sludge arriving at the SHDF (Sludge Main discharge) to better estimate the requirements for a sludge thickening system and thickening recycle water treatment and handling needs. § Determine BSPS pumping characteristics especially at higher flowrates and with sludge having less solids content than historically pumped.

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Anaerobic Digestion This section includes evaluation of anaerobic digestion options for thickened raw sludge. Digestion process alternatives are numerous, and include options to achieve Class A biosolids. In addition to digestion process options, this section includes evaluation of processes that are closely related to digestion such as pre-pasteurization or other pre-digestion processing of sludge to create Class A material or to improve digestion process performance. This section is outlined as follows:

1. First, a discussion of struvite/scale is included since this has become a significant issue at the SHDF.

2. Following struvite, a discussion of several pre-digestion processes such as debris removal, pre-pasteurization and related systems is included.

3. Digestion process evaluation includes several different systems including processes which achieve Class A biosolids either directly or indirectly.

4. Finally, other systems are included such as digested sludge storage and chemical addition.

Struvite Production and Control Struvite normally occurs as a tenacious scale material, forming mostly in anaerobically digested sludge piping and downstream processes such as sludge lagoon piping or digested sludge dewatering systems and dewatering centrate piping. Struvite scaling can also occur within digesters, sometimes forming large scales on the bottom of digester covers, or scale buildup on draft tubes.

Struvite Formation. Struvite is a compound comprised of magnesium, ammonium and phosphate salts complexed with water [MgNH4PO4.6H2O]. It is formed of 1:1:1 stoichiometric ratio of NH4:Mg:PO4:

+2 +-3 Mg + NH4 + PO44 = MgNH PO 4

Activities of these ions are affected by pH, ionic strength, complexing agents, temperature, and total component concentration. Actions which can enhance struvite precipitation are:

1. Raising pH, either by adding a base or by stripping carbon dioxide from solution. Reduced solubility of struvite occurs as pH rises.

2. Increasing the concentrations of one or more of the components, magnesium, ammonium, or phosphate.

3. Reducing, or less likely, increasing, the liquid temperature from 30°C, the temperature of apparent maximum solubility.

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The opposite actions will tend to reduce or eliminate struvite precipitation.

- 3- 2- In anaerobic digesters, high concentrations of anions such as HCO3 , PO4 , S , and cations such as Mg2+, Ca2+, and NH4+ can result in supersaturated conditions with respect to various solids as indicated in Table 6-7.

Table 6-7. Possible Precipitants for Conditions Within Anaerobic Digesters Phosphate Precipitant Precipitates That May Form Ca(II) Various calcium phosphates eg.

B-tricalcium phosphate: Ca3(PO4)2(s)

hydroxyapatite: Ca5(OH)(PO4)3(s)

dicalcium phosphate: CaHPO4(s)

calcium carbonate: CaCO3(s)

Fe(II) ferrous phosphate: Fe3(PO4)2(s) a ferric phosphate: Fex(OH)y(PO4)3(s)

ferrous hydroxide: Fe(OH)2(s) a ferric hydroxide: Fe(OH)3(s)

Fe(III) ferric phosphate: Fex(OH)y(PO4)z(s)

Al(III) aluminum phosphate: Alx(OH)y(PO4)3(s)

aluminum hydroxide: Al(OH)3(s) a Formed by oxidation of Fe(II) to Fe(III) during the treatment process

Struvite formation is not usually encountered when an anaerobic digester is receiving sludges from a plant where iron salts are being used for phosphorus precipitation, or where ferrous or ferric salts are being added to wastewater to improve clarification since iron dose is relatively high in these cases. These cations compete successfully for phosphate and prevent struvite formation. The addition of Fe(II) or Fe(III) to either wastewater or to an anaerobic digester contents is an accepted method of preventing struvite formation.

Another major potential for struvite precipitation is in high speed centrifugation when used for dewatering anaerobically digested sludge. The high G forces developed in these machines strip out carbon dioxides, increasing pH and promoting the formation of struvite in the machine and centrate piping. The addition of polymer typically tends to increase pH further aggravating the scaling problem. Struvite formation has been experienced in high solids centrifuges installation at treatment plants including the following: Denver Metro, Chicago Calumet, and the John Eagan plant in Shaumberg, Illinois. Each has resorted to control measures. Denver adds ferric chloride (1,000 mg/L) to the feedstock sludge and has installed glass lined centrate piping. Chicago uses carbon dioxide, injected into the sludge, to lower the pH to about 6.8 prior to polymer addition.

The Chicago approach is costly using refrigerated CO2 storage, vaporization, depressurization, and injection equipment. The Eagan Plant uses ferric chloride (2,000 mg/L) with injection into the feedstock, the centrifuge, and the centrate piping.

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Options for Struvite Control. A range of options exist to counter the effects of struvite precipitation. They fall into two main groups: prevention, and controlled stimulation of struvite precipitation at an advantageous location.

§ Prevention – the Most Common Approach. Options include pH reduction with acid or carbon dioxide, construction of systems that preclude uncontrolled carbon dioxide release, dilution to reduce component concentrations, use of antiscaling chemicals, minimizing phosphate production within digesters or discharge to digesters, and addition of chemicals to form phosphate precipitates that are softer and easier to clean than struvite. § Controlled Precipitation. Options include the addition of appropriate quantities of magnesium and phosphorus to achieve complete precipitation of phosphorus or ammonia, or, in cases where struvite precipitation is difficult or too costly to avoid, the construction of facilities to allow relatively simpler cleaning.

The practicality of these schemes can be evaluated with any of several chemical equilibrium models, including the Electrical Power Research Institute's SEQUIL, the U.S. EPA's MINTEQA1, and the U.S. Geological Survey's SOLMINEQ.88. These models predict the amounts of chemical precipitates (including struvite) that could be formed under specific treatment conditions, the quantities of treatment chemicals required to achieve those conditions, and the pollutant conditions.

Suggested Investigations. The recent cleaning of Digester 7 at the SHDF (May 2003) indicated large piles of scale material on the floor of the digester. This is a very unusual situation. The location and type of material suggests that struvite (or another phosphate-based scale material) is forming within the mass of sludge, perhaps around tiny grit particles in the digester. When the scaled up particles become large enough they settle out of the suspended mass and are deposited on the digester floor, and are scoured into piles where digester mixing energy is lowest. This rather extraordinary situation may be caused by large production of orthophosphate within the Sludge Main due to the specific biological conditions and long time of transit within the pipeline. Testing needs to confirm this scale-production situation as well as the specific scale material which is forming within the digesters.

Limiting phosphate production within the Sludge Main could be a viable control method. Also, iron addition could also be a major control option for the digesters.

Sampling and analytical work is needed to confirm the struvite (or other scales) being formed, the reasons for formation, and the control options which will be most viable and cost-effective. Chemical equilibrium modeling for scale compounds has been shown in other projects to be of considerable help in understanding the situation and in controlling it.

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Debris Processing and Removal Debris in raw sludge includes non-digestible solids such as plastics, woody or cellulose products, rags, hair, and vegetal and stringy material. Grit is sometimes considered debris material, however there is no feasible method to remove grit from thickened sludge, and, therefore, its removal is not considered after thickening. However, prior to primary sludge thickening, grit removal can be conducted.

Debris is best removed prior to digestion so that impacts on sludge pumping and heat exchanger operation are minimized. However, many agencies grind the debris within sludge and allow it to pass through the system and become part of final biosolids materials.

Influent Screening. The following influent screening factors are critical in evaluation of sludge debris handling/removal:

§ The Las Vegas Street WWTP headworks includes barscreens with 3/4-inch spacing. This obviously removes larger material, however, much debris material makes it through this type of screening. § The future Northern Water Reclamation Facility is anticipating influent screening using 6 mm-spaced step screens. So, the sludge from this plant and other potential WWTPs that may have their sludge sent to the SHDF, will probably have similar debris removal systems as the current Las Vegas Street WWTP. § Reducing the size of influent barscreen width would reduce the amount of debris in sludge. This is an issue that could be important in the long-term, but we believe it is beyond the scope of this Masterplan for the SHDF.

Debris Handling/Removal. The current digestion system at the SHDF includes grinders for debris handling. However, debris (plastics) have been a problem in the past on FSB surfaces. Also, the standpipes on the new digesters occasionally plug up. It is recommended that sludge screening should be installed at the BSPS. This recommendation will be included in the ongoing Las Vegas Street WWTF.

If biosolids products will be produced in the future for off-site use, then sludge screening to reduce debris content should be undertaken. The Parkson Strainpress is a sludge screening system that has good history of removing such debris. Normally it is used with 5 mm spacing on thickened primary sludge. It is possible that this type of process could be implemented at the Las Vegas Street WWTP on the thickened or semi-thickened primary sludge. Such a screening system would need to have at least two units and have associated sludge feed systems, screenings handling/loadout, odor control, and related systems. A new or modified structure would be required.

Grit Removal. Grit is removed at the headworks of the Las Vegas Street WWTP. Other WWTPs that will be sending sludge to the SHDF will include similar grit removal systems. However, these grit removal systems can become overloaded during peak events such as during storms, or they sometimes may not operate at optimal performance. Also, smaller grit material makes it through

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common grit removal systems in any case. The net effect of these factors is that smaller grit material is moving through the sludge system currently. The larger of this material probably ends up in the digesters where some of it collects on the digester floors over the years. This is generally not a problem, and such grit material is removed whenever the digester is cleaned (perhaps on 5-year or similar cycles). The most critical problem would be if peak or unusual grit loads are discharged to the SHDF, where an excessive quantity could plug the Sludge Main, as occurred in a 1999 storm- related event. Operational procedures are now used to try to prevent this type of event from recurring.

Disintegration Using Ultrasound Technology Ultrasound sludge disintegration technology has been developed in Europe to achieve improved anaerobic digestion performance. There are two primary commercial systems currently promoting ultrasound treatment in North America: (1) the Sonix system by W. S. Atkins of the UK; and (2) the IWE system marketed through RDP in the U.S. No full-scale permanent system is yet operating in North America.

Full-scale testing work was completed at the Orange County Sanitation District (OCSD) in 2002. This testing was completed with a Sonix V5 unit that was used on the thickened waste activated sludge (TWAS) feed to one digester. The digester was fed increasing proportions of sonicated TWAS, and decreasing proportions of primary sludge. Testing reached WAS proportions of 60 to 65 percent of the total sludge mass fed to the digesters (35 to 40 percent primary sludge mass). For unsonicated WAS feed to digestion, the control digester showed worsening performance as the proportion of WAS increased, confirming OCSD’s historical experience that WAS proportions over about 25 percent caused significantly poorer performance in their digesters. The primary result from OCSD’s standpoint was that the digestibility of sonicated WAS material appeared to become similar to digestibility of primary sludge, which increased volatile solids reduction of WAS material by perhaps 50 percent. Gas production increased commensurately. OCSD intends to implement the technology at one of its plants within the next year or so.

European Experience. Sonix reportedly has a few full-scale systems operating in northern Europe and the IWE system is reportedly operating at about a dozen plants in Germany and Austria. Reasons for implementation of the technology in Europe are as follows:

§ Increased volatile solids reduction (VSR) within digestion § Increased digester gas production for energy value § Indications of improved dewatering performance and maybe improved foam control within anaerobic digestion

Under some situations in Europe, it appears the vendors are guaranteeing results in terms of increased VSR and gas production, and perhaps better dewatering performance, too.

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Evaluation for Colorado Springs Utilities. Normally, ultrasound/sonication has been implemented on thickened WAS since that provides the best payback. However, using this technology on raw WAS prior to pumping through the Sludge Main, would no doubt increase the acidification/fermentation phase of digestion already occurring in the Main. This is likely to cause faster reaction rates which generate more gas during pipeline transit. These are highly undesirable consequences. Therefore, upstream use of sonication at Las Vegas Street WWTP or other WWTPs is not advisable.

Implementing ultrasound/sonication after Sludge Main transit could be considered. However, with this approach, primary sludge is now mixed with the WAS, and even small amounts of debris are a major problem with current sonication systems (the systems utilize equipment placed within sludge forcemains thus allowing any debris to collect on the equipment). Therefore, use of ultrasound/ sonication technology at this time does not appear feasible or cost-effective. However, as the technology is implemented in North America in the next several years (very likely to occur), and with possible technology improvements over time, there is a chance that it could ultimately prove advantageous for Colorado Springs Utilities. Therefore, Colorado Springs Utilities should continue to monitor the development and use of this technology.

Thermal Hydrolysis Thermal hydrolysis of raw wastewater sludge has been developed commercially as the Cambi process, a Norwegian-based company of the same name. The Cambi process performs thermal hydrolysis in a batch step at elevated temperature and pressure such that it is a Class A process. The Hamar, Norway plant has now been operating about 7 years using the Cambi process and several more Cambi facilities have recently come on-line in Northern Europe (in Denmark, the UK, and Dublin, Ireland). To date, there are no Cambi facilities in North America, although pilot testing is being conducted on the process at San Francisco’s Southeast WPCP in 2001 and 2002. The process has similarities to the heat treatment processes implemented 20+ years ago at many plants in North America. However, the temperature and pressure of this newer hydrolysis system are not as high as used in previous heat treatment systems.

Several papers describing the Cambi process are available. It is being marketed and sold in the US through an agreement with RDP. Economic analysis of the process for San Francisco shows that it may have promise. However, there are several concerns about the technology that make it difficult to consider:

1. It involves a pre-dewatering step prior to hydrolyzation. This would be a large raw sludge dewatering system at the SHDF, and would add another large process to be operated and maintained.

2. The pressurized reactors, steam system, flash tank, and related systems represent new and different technological systems for wastewater agencies in this country – creating problems for operation and maintenance unless the system is privatized.

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3. Odor controls for the process would need to be very effective at the SHDF, providing final high temperature oxidation of the foul gas in regenerative thermal oxidizers (RTOs) or similar systems.

An advantage of the Cambi process would be reduced size required for the digesters. However, this does not offset the fact that the system is not proven outside of Northern Europe. Therefore, this process is not recommended for consideration at this time.

Pre-Pasteurization Pre-pasteurization of raw sludge prior to mesophilic anaerobic digestion is an option available for use in achieving a Class A process/product. Pre-pasteurization has been typically implemented at 70 degrees C for 30 minutes, although the new EPA time/temperature equation for slurries (less than 7 percent solids) would allow 67 degrees C for 30 minutes, or other time/temperature such a 65 degrees C for about one hour, 60 degrees C for 5 hours, or 55 degrees C for 24 hours, or other combinations – refer to the time/temperature equations plotted on Figure 6-2.

75 uEPA, >7% solids 6 FDA, eggnog past. EPA, <7% solid 70 u l 6 Fuchs, “conservative n recommendations”

C l o Ondeo PFRP (2002) 65 s

60 n n Temperature,

55 s n n u 50 l 0.4 0.7 1 2 4 7 10 20 40 70 100 Contact Time, hours Figure 6-2. EPA Alternative 1 Time/Temp Equation Comparisons

Pre-Pasteurization Experience. The primary experience for pre-pasteurization is in Europe starting in the 1970s and extending through the 1980s. Most of the experience has been in Switzerland, Germany, and Austria at relatively small plants where the disinfected digested sludge was used on pasture and related lands. A few larger pre-pasteurization facilities at larger plants were built at Zurich, Switzerland and Capetown, South Africa, but the Zurich system has been shut down and the status at Capetown is unknown. It is hard to determine the long-term reliability of these previous systems, but it appears they were not designed or operated with the degree of temperature control, reliability, and redundancy that would be required to meet EPA Part 503 rules. The pre- pasteurization tanks would need to be strictly batch-operated to avoid any short-circuiting of solids.

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In addition, “every” batch needs to meet the time/temperature requirements and plants must monitor and record data for the pre-pasteurization operation to prove (upon EPA or state audit) that temperatures and times have been met.

Experience in North America is very limited for pre-pasteurization. There are reports of at least one failed system in recent years – failure is reportedly due to lack of strict batch tank configuration. Several wastewater agencies are pursuing pre-pasteurization systems in the US, and some appear to be under construction.

Pre-Pasteurization System. A pre-pasteurization system at the SHDF would need to have multiple batch pasteurization tanks – probably at least 4 or 5 such tanks. Raising temperatures to the 65 to 70 degree C range is challenging but can be accomplished with direct steam injection. The greater challenge is cooling the sludge from these high temperatures down to mesophilic digestion temperatures (37 degrees C). The heat exchanger system required would be very large and would represent a challenging operation. Since direct sludge/sludge heat exchange is not recommended, there would need to be a sludge/water/sludge or other system used, thus requiring many heat exchangers to dump the recovered heat into the raw sludge or use/dispose this heat in some other manner. Space for the number of heat exchangers would require substantial additional building space.

Reliable valve operation for 0.5 to 1 hour batch operation becomes more questionable due to frequent use of valves and due to limited times between batches to correct any problem that could occur. Foul air collection and treatment of the pre-pasteurization tank gases would also be required. An analysis of this type of pre-pasteurization system was completed for the San Francisco Southeast WPCP digestion project in 2001. The outcome indicated that the system proposed for TPAD Class A (using batch tanks following thermophilic digestion) described later in this Chapter, has roughly similar overall life cycle costs to a pre-pasteurization system, and has considerably less risk and much greater reliability of consistently meeting time/temperature requirements for Class A.

Another factor in selecting the post-thermophilic batch concept over the pre-pasteurization concept is that there are VSR benefits. Pre-pasteurization achieves some degree of hydrolysis, but previous work shows that this does not result in much overall digestion VSR improvement over conventional mesophilic digestion – i.e., perhaps a 1 percentage point improvement in system VSR could be expected, thus moving from 50 to 51 percent VSR in the digestion system. In comparison, as described later, the performance of thermophilic digestion coupled with Class A batch tanks is estimated to achieve a several percentage point gain in VSR. Therefore, based on previous assessments, we recommend that pre-pasteurization be dismissed as a potential Class A digestion technology, in favor of other approaches using thermophilic digestion.

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Digestion Process Evaluation In addition to mesophilic digestion (either single or 2-stage), advanced anaerobic digestion processes evaluated here are grouped into the following classes and are schematically represented in Figure 6-3:

§ Acid/gas phased digestion. This category can include either phase (acid or gas phases) at mesophilic or thermophilic temperatures, but is most often being implemented with both phases at mesophilic temperatures due to simplicity in sludge heating and cooling. There is also a variation called “three-phase digestion”. Three- phase digestion is a combination of acid/gas phased digestion and temperature phased digestion. Class A digestion can be accommodated if there is a thermophilic stage. § Thermophilic digestion. Although single stage thermophilic would be the simplest form of thermophilic digestion, most plants using thermophilic digestion have moved to “staged thermophilic” digestion for improved pathogen destruction. Also, batch tanks can be added or other accommodations made within the digestion process to provide a Class A digestion system. § Temperature phased digestion. This has been implemented most often with thermophilic digestion as the first phase, followed by mesophilic digestion as the second phase. The primary reason for this order is to produce a final product with minimal odor level since thermophilic digestion product has been described as odorous by some. As with thermophilic digestion, batch tanks or other methods can be used to insure a Class A process.

The principal reasons to consider advanced digestion processes are to achieve greater VSR, more gas production, and Class A digestion. Before evaluating the various advanced digestion options, a review of the current digestion system is included.

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Figure 6-3. Process Schematic Diagrams – Advanced and Phased/Staged Digestion

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Current Anaerobic Digestion System The existing digestion system operated by Colorado Springs Utilities is essentially a two-phase system described as follows:

§ The first-phase of the system involves fermentation, acidification, and hydrolysis of raw sludge within the Sludge Main. This is often referred to as acid phase digestion. It is being conducted at ambient temperature and is within a long pipeline, thus providing a plug-flow system rather than a complete mix system as found within digestion reactors. § The second phase is the anaerobic digestion system being conducted within the digesters at the SHDF at mesophilic temperatures (35 to 38 degrees C). The Solids Retention Time (SRT) has recently been about 25 days within this digestion system. VSR for the current system is about 51 percent average, however, the older digesters, which use gas mixing, are showing VSR of about 55 percent, and the newer digesters, with mechanical propeller mixing, are showing VSR of only about 48 to 49 percent. These VSR calculations do not take into account the digestion occurring within the Sludge Main. This digestion system was not specifically designed for this two-phase operation, but it is occurring and it has probably aided in achieving slightly improved digestion performance (i.e., greater VSR) over a system that did not have the pipeline acid phase digestion process prior to the methane digesters.

Acid Digestion Within the Sludge Main The acid digestion occurring within the Sludge Main is relatively uncontrolled. Temperature of the sludge is probably close to the temperature of the wastewater, and the sludge temperature is not likely to change much during pipeline transport since the ground temperature around the Sludge Main is probably not greatly different than the sludge temperature on a seasonal basis. With the advent of transit time increases to 48 hours in the last 2+ years, much more gas production is occurring within the Main. This is consistent with acid digestion principles, and the gas should contain mostly carbon dioxide, with smaller quantities of nitrogen, hydrogen, and some methane. However, having significant gas production within the Sludge Main is an operating problem, and, therefore, acid digestion needs to be limited by reducing the transit time (i.e., increasing the sludge flowrate through the Sludge Main, as discussed in the previous section, Pumping and Thickening Raw Sludge).

Normally in acid digestion reactors, a 1 to 2 day SRT is used at mesophilic temperatures to achieve VFA concentrations of 5,000 mg/L and even higher, a pH of less than 6, and gas production that is about 60 to 70 percent carbon dioxide. Acid phase digester loading rates are often about 2 pounds VS/cubic foot/day and 5+ percent solids feedstock is often needed to achieve the high loading rates for optimum acid phase digestion. Increasing the temperature of the sludge in the Main, or using other methods to achieve better acid phase digestion within the pipeline, would only produce more gas. Also, the solubilization of phosphate during Sludge Main transit appears to be a factor in

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increasing the struvite problem in the digesters. Therefore, the current pipeline acid reactor is not capable of being operated at optimum acid phase digestion conditions.

Another factor to consider is that hydrolysis during Sludge Main transit is solubilizing some of the volatile solids. With future raw sludge thickening at the SHDF, solubilized material (VFAs, etc.) will be lost to the thickening centrate and will not end up in the digesters to produce methane gas. Therefore, reducing hydrolysis during pipeline transit is a desirable approach – and this would be achieved by increasing the sludge pumping rate through the Sludge Main.

Acid/Gas Phased Digestion at the SHDF Creating a controlled acid/gas phased digestion system at the SHDF would involve several modifications. The primary modification would be that all sludge arriving at the SHDF would be directed to an acid phase digester to continue the reactions that have begun within the Sludge Main. The purpose of this approach would be to achieve maximum benefits from acid phase digestion, before directing the sludge to the methane digesters.

In this process, the acid phase has a short SRT and low pH as discussed previously. The methane phase has fully developed methanogen levels with longer SRT (12 to 15 days minimum) and full methane production with pH in the range of 6.8 to 7.5. Table 6-8 includes performance data from plants or pilot plants utilizing three different temperature configurations:

§ Mesophilic acid phase followed by thermophilic gas phase (acid/gas phased at meso/thermo) § Mesophilic acid phase followed by mesophilic gas phase (acid/gas phased at meso/meso) § Thermophilic acid phase followed by mesophilic gas phase (acid/gas phased at thermo/meso)

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Table 6-8. Advanced Anaerobic Digestion Process Information HRT (days) Process VSR for Type of in Each Temps Reactor VSR Mesophilic Process/Plant Sludge Stage (°C) Feeding (%) Digestion Staged Thermophilic Vancouver, Canada P+TF/SC 17-Th All stages Continuous 62 to 63 47 Annacis Island Plant 2-Th 55 to 56 2-Th 2-Th Mason Farm WWTP 10 percent 19-Th All stages 10 hrs/day 65 43 OWASA, NC Fermented P 10-Th 56 to 57 1st stage, 90 percent 10-Th Batch 2nd stage WAS Vancouver, Canada P only 22-Th 55 Continuous 67 to 70 57 Lions Gate WWTP 22-Th Both stages SSb Thermophilic with Storage Aalborg, Denmark P+WAS SS Thermo 52 to 55 Hourly Feed “Significantly” Unknown AalborgWest WWTP 15-Th Sequence greater than SS (plus short Meso meso storage) Temp-Phased Thermo/Meso WLSSD, WAS-only 8-Th 55-Th Continuous 46 40 Duluth, MN 23-M 37-M King Co., WA P+WAS 8-Th 55-Th Nearly Continuous 68 58 Renton (Pilot Scale) 16-M 37-M Neenah-Menasha, WI P+WAS 16-Th 55-Th Nearly Continuous 58 50 16-M 36-M Madison, WI Pilot (Lab P+WAS 5-Th 55-Th Intermittent 64 58 Scale) 15-M 35-M City of Los Angeles P+WAS 10-Th 55-Th Intermittent 66 48 Hyperion WWTP (pilot- 7-M 35-M scale) Cologne, Germany WAS-only 7-Th 55-Th Continuous 43 34 Stammheim Plant 27-M 35 to 38- M Sturgeon Bay, Wisconsin P+WAS ~ 17-Th 55-Th Intermittent 65 62 (at much > 20-M 35-M longer SRT) Acid/Gas Phased at Meso/Thermo DuPage Co. Illinois WAS-only 2-Acid 37-Acid Continuous 62 to 63 ~45 16-Gas 52-Gas (plus storage (38 to 43 of 4 to 10 storage) days) Acid/Gas Phased at Meso/Meso San Bernardino, CA P+WAS 2 to 3 (acid) 35 acid Continuous 57 53 25 (gas) 35 gas Elmhurst, Illinois P+WAS 1-Acid 30-Acid Batch Acid 50 36 38-Gas 36-Gas

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HRT (days) Process VSR for Type of in Each Temps Reactor VSR Mesophilic Process/Plant Sludge Stage (°C) Feeding (%) Digestion DuPage Co., Illinois WAS-only 2 (acid) 36 acid Continuous 59 ~45 16 (gas) 36 gas (plus storage of 4 to 8 days) Madison, WI P+WAS 1 to 2-Acid 35-Acid Twice/day 58 57 (Lab-Scale Pilot) 15 to 20-Gas 35-Gas Acid/Gas Phased at Thermo/Meso City of Los Angeles P+WAS 2 (acid) 55-Th Intermittent 50 48 Hyperion WWTP (pilot 12 (gas) 35-M scale) Indianapolis, IN P+WAS 2 (acid) 55 & 60- 2 or 4 times a day 55 to 60 Unknown Belmont WWTP 10 (gas) Th (IDI Pilot Scale) 37-M Three-Phase Digestion Inland Empire P+WAS 3-Acid 33/38- Nearly Continuous 56 54 Utilities Agency, CA 12/14-Th Acid Reg. Plant #1 14/16-M 53/55-Th 39/44-M Notes: VSR = Volatile Solids Reduction Mesophilic = Meso = M P = Primary Sludge SS = Single Stage Thermophilic = Thermo= Th WAS = Waste Activated Sludge TF/SC = Trickling Filter/Solids Contact

Table 6-8. Advanced Anaerobic Digestion Process Information (continued) How VSR Dewatering Extent Process/Plant Calculated Performance of Data Comments Staged Thermophilic Vancouver, Canada Van Kleeck 32% cake solids content, 3 years Extensive data. Consistent long-term Annacis Island Plant high solids centrifuges, performance. Class A process in British 95% capture Columbia. Mason Farm WWTP Mass Balance No dewatering 1 year Meets Class A time/temp Batch OWASA, NC operations. Requirement in 2nd stage. Vancouver, Canada Van Kleeck Centrifuges, 37% cake 8+ years of Steady performance on primary sludge Lions Gate WWTP solids, 95% capture operation only. Pathogen data suggest Class A product. SSb Thermophilic with Storage Aalborg, Denmark N/A Belt Filter Presses, 25% 1 year VSR is not calculated, but plant reports AalborgWest WWTP cake solids, 10 kg/tonne “significant” more gas and power polymer production from thermophilic over prior mesophilic operation. Temp-Phased Thermo/Meso WLSSD, Mass Balance High-solids centrifuges, 1 year Large pulp/paper load on WWTP-So, WAS Duluth, MN 28 to 30% cake solids, is less digestible than normal WAS. 99% capture

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How VSR Dewatering Extent Process/Plant Calculated Performance of Data Comments King Co., WA Mass Balance Lab-scale Belt Press got Several months Well-run and extensive pilot test. Renton (Pilot Scale) 16% cake solids – same as full-scale mesophilic Neenah-Menasha, WI Van Kleeck 20% cake solids content 2 years Pleased with TPAD. Improved VSR. Belt Filter Press Dewatering approved “a few” percentage points in cake solid. Madison, WI Pilot (Lab Van Kleeck Thickening tests Several months Extensive pilot testing of many different Scale) conducted. scenarios. City of Los Angeles Mass Balance Not Reported 6 months City reported best results for VSR was Hyperion WWTP (pilot- operation obtained with this process. scale) Cologne, Germany Van Kleeck Centrifuges, 33%t cake 3 years average Large plant using egg-shaped digesters. Stammheim Plant solids, 8 kg/tonne Limited VSR due to all-WAS feed and long polymer sludge age. Sturgeon Bay, Wisconsin Mass Balance Belt Filter Press, 13 to 4 years Small plant with very long detention times. 15% cake solids Data 2001. Acid/Gas Phased at Meso/Thermo DuPage Co. Illinois Mass Balance 21% cake solids on belt Several years of Acid/Gas phasing solved the large foaming filter presses full-scale data problem and improved performance significantly with WAS-only sludge. Acid/Gas Phased at Meso/Meso San Bernardino, CA Mass Balance Centrifuges 25%cake Several months Poor mixing in acid digester has allowed solids, Belt Press 19% debris accumulation. cake solids Elmhurst, Illinois Unknown Belt Filter Press, 20% Several months Batch acid operation causing foam in gas cake solids content of data digesters. Acid reactors are new. DuPage Co., Illinois Mass Balance Belt Filter Press, 20% Several months Acid gas phased digestion provided cake solids of pilot and performance improvement and foam full-scale data control. Madison, WI Van Kleeck Thickening tests Few weeks of Part of extensive pilot testing program. (Lab-Scale Pilot) conducted data. Acid/Gas Phased at Thermo/Meso City of Los Angeles Mass Balance Not Reported Several months Process did not appear to stabilize and was Hyperion WWTP (pilot discontinued after several months. scale) Indianapolis, IN Mass Balance Not Reported Several months Batch thermophilic acid phase proven as Belmont WWTP at varying site-specific PFRP equivalent. (IDI Pilot Scale) conditions Three-Phase Digestion Inland Empire Unknown Belt Filter Presses, 19% Several months Temperatures are not consistent. Final Utilities Agency, CA cake solids (with 3-phase) of data phase is hotter than typical meso systems. Reg. Plant #1 versus 17% cake solids with SS Meso Source: Schafer, P., J. Farrell, G. Newman, S. Vandenburgh, 2002. Advanced Anaerobic Digestion Performance Comparisons. Presented at WEFTEC Conference, Chicago, Illinois, October 2002.

The wastewater plant with the longest operating experience with acid/gas phased digestion is the Woodridge-Greenevalley plant of DuPage County, Illinois. This plant operated with both phases at mesophilic temperature many years ago, but has operated under the meso/thermo configuration for almost 10 years. There is a reactor following the thermophilic phase that is primarily a digested sludge storage tank. The temperature of the sludge in this tank is typically at elevated mesophilic

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temperatures, but some limited additional biosolids stabilization reportedly occurs in this tank. The reported performance data for this digestion system does not take this storage reactor into account.

The acid/gas phased digestion process performance at DuPage County has been beneficial, reportedly resolving a substantial foaming problem in the digesters and providing major improvement in VSR. The high ammonia recycle in the dewatering filtrate has been a significant problem for the plant in meeting its ammonia discharge standards.

Several plants are operating in the meso/meso configuration and data from some of the plants and one pilot program are shown in Table 6-8. Some of the comparison work is showing relatively little VSR improvement from acid/gas phased digestion, while other plants show significant VSR improvement. No factor or reason has been identified to account for this variation in performance.

It is clear that the acid phase digester needs to be designed to account for the specific needs of this process. This includes adequate precautions for grit and debris accumulation or removal since all sludge is directed through this reactor. In addition, handling of the gas from this phase needs careful consideration since it will probably contain low methane content and perhaps high hydrogen sulfide content. Combustion of the acid phase digester gas has been a problem at several of the plants attempting to implement the process – due primarily to the low BTU content, whereby natural gas has been required to insure continuous combustion. Also, the high hydrogen sulfide content of several thousand parts per million is likely to be a problem at the SHDF with total sulfur emission limitations.

The configuration of the acid phase reactor has also received a great deal of attention in recent years since some plants which used conventional-shaped digesters for acid digestion have had major debris buildup problems. A vertically-oriented silo-shaped reactor has been recommended as a more appropriate shape for the acid phase reactor and this shape is being tested in 2003 at the Baltimore (Maryland) Back River WWTP. Startup problems have prevented the system from providing good information thus far.

In general, acid/gas phased digestion is not a well-developed process at this point, especially for plants containing mixed primary and WAS sludges. Testing at Baltimore and Phoenix in the next few years should provide substantially more information about how the system operates with primary sludge and the advantages and disadvantages of the process. At this time, considering the partial acid-phase digestion that is already occurring within the Sludge Main, the unusual phosphate/struvite problem, gas handling concerns, and the uncertain future of a more formal acid/gas phased digestion system, we do not recommend pursuing this process for the SHDF.

Thermophilic Digestion Several agencies have transformed their mesophilic digestion systems to thermophilic digestion in recent years to improve VSR and pathogen control. The range of temperatures typically used for thermophilic digestion is between 50 and 57°C (122 to 135°F), although for agencies using thermophilic digestion as part of a Class A process, temperatures have typically been in the range of

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53 to 56 °C. As shown in Table 6-8, the North American agency that has led this effort in the last decade has been the Greater Vancouver Regional District (GVRD) in British Columbia, Canada. In the early 1990s, GVRD began 2-stage thermophilic digestion at the Lions Gate plant, primarily with the objective of creating pathogen-free biosolids for beneficial use purposes. This experience provided the impetus for the larger and more definitive 4-stage thermophilic digestion process at the Annacis Island plant in the mid-1990s. Both plants have seen significant increases in VSR, as indicated in the table, as well as providing pathogen-free product for successful biosolids beneficial use programs.

The OWASA facility in North Carolina (Mason Farm plant) is also showing large increases in VSR by switching to a staged thermophilic process. However, part of this increase is due to longer solids retention times within the process. This plant had difficulty in consistently meeting the 38 percent VSR regulatory requirement prior to the change to thermophilic digestion. A 22-hour/day batch operation in the second stage reactor of the new system insures meeting the time/temperature requirements for Class A biosolids (see Figure 6-2 shown previously).

Two of these four thermophilic digestion facilities (Aalborg and Annacis Island) have historically recovered at least part of the heat through sludge/sludge heat exchangers from thermophilic digestion, and OWASA is planning to recover this heat to help heat incoming raw sludge. However, several plants have found heat recovery from thermophilic digestion to be difficult and some plants have abandoned efforts to recover heat.

At the Lions Gate plant, the digested product is dewatered at 55º C (131 °F) and the cake trucked off-site. The dewatered cake at Lions Gate is reportedly more odorous than mesophilic digested cake product, and the centrate is very odorous. At the OWASA plant, the thermophilic digested sludge has been stored in large storage tanks for 20 days or longer. These tanks lose temperature to the environment so that the final slurry product trucked to reuse sites is at approximately mesophilic temperatures. This final reuse product at OWASA has reportedly little odor difference from the previous mesophilic digested slurry product.

The City of Los Angeles has implemented Class A thermophilic digestion in 2002 at both its WWTPs – the large 400-mgd Hyperion Treatment Plant and the smaller Terminal Island Treatment Plant. At Hyperion, second stage thermophilic digesters are operated with a batch time of 24 hours at 55 degrees C to meet the EPA’s time/temperature equation shown previously (Figure 6-2). The odor of the thermophilic digested dewatered products at these plants has not been a problem for agricultural reuse in Southern California. Users have reported that the thermophilic Class A cake actually had less odor than the previous mesophilic dewatered cake products.

Ammonia levels are higher in thermophilic digested sludge (and in dewatering filtrate/centrate) than in the previous mesophilic digested sludge from these plants. This is caused by increased reaction rates, slightly increased VSR, and thus greater ammonia production. This normally-small increase in ammonia levels has not been a problem at most plants, but could be an issue for plants that have marginal capacity to handle additional nitrification.

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Thermophilic digestion in a staged system may be an attractive option at the SHDF, especially if Class A digestion can be achieved with little complexity and at reasonable cost.

Temperature Phased Digestion About a dozen agencies in the US have now implemented temperature phased digestion, and performance data for several of these plants are included in Table 6-8. In addition, data from three pilot scale programs for temperature-phased digestion are included in the table because of the availability of comparative performance results. The comparative results show typically good performance improvement from prior mesophilic digestion to temperature phased digestion. These temperature phased digestion facilities are all achieving increased VSR and gas production.

It is interesting to note the large variety of SRTs being used by these temperature phased digestion plants. SRTs in each phase are often dictated by the size of digesters available at the plant since the only temperature-phased plant listed in Table 6-8 with new digesters is the Western Lake Superior Sanitary District plant at Duluth, Minnesota. In most cases for full-scale operations, the SRTs are substantially longer than required for stable operation.

Thermophilic sludge heat recovery is practiced at most of the full-scale temperature phased digestion plants listed in Table 6-8, however the methods of heat recovery are different. Direct sludge/sludge heat recovery is practiced at Sturgeon Bay and some other plants. The 100-mgd Cologne-Stammheim plant (Germany) utilized a sludge/water/sludge heat recovery system with concentric tube heat exchangers for many years, however, this particular plant has just recently abandoned its temperature phased digestion process.

Agencies operating temperature phased digestion report that the dewatered cake product is well- stabilized and has the typical odor of mesophilic digested biosolids, although a frequent comment is that ammonia odor from the product is stronger than from the previous mesophilic digested product. This appears to occur because of the following: (1) higher ammonia concentrations in temperature phased digested biosolids, and (2) higher pH of the biosolids, resulting in a greater percentage of ammonia in the molecular form. The greater ammonia concentrations in dewatering centrate/filtrate are causing concern in some of these plants in meeting current or expected future ammonia discharge limits from the wastewater treatment plant.

Achieving Class A Within Thermophilic Digestion Systems Class A digested biosolids can be developed in several different ways at the SHDF and there are pros and cons for each method. The following provides an outline of the different approaches:

§ Strict use of EPA’s Class A Alternative 1 time/temperature equation in Part 503 means that the agency is assured that Class A biosolids are being produced as long as the required time and temperature is achieved for all sludge particles (i.e., no short- circuiting through the process). A typical thermophilic digestion temperature of 55 °C requires a 24 hour batch time. This batch time can be developed within

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separate batch tanks or within sequencing batch-operated thermophilic digesters. Or, a 2-stage thermophilic digestion system is possible, whereby the second stage includes the required batch operation. § Since the above batch-operated systems represent significant increased complexity of operation, several agencies are experimenting with less-than-required time/temperature and simplified systems to achieve Class A. This can work partly because the EPA Class A time/temperature equation has been shown to be very conservative when used within thermophilic sludge digestion. Some agencies such as Inland Empire Utilities Authority and the City of Los Angeles are using EPA’s Class A Alternative 3 approach, although EPA has indicated this may not be the best approach and various EPA staff have made statements that Alternative 3 may be eliminated at some date from the Part 503 rule. § Research by Columbus Water Works (Georgia), Brown and Caldwell, and University of North Carolina is underway which is showing that a complete mix thermophilic digestion system at greater than about 6 days of SRT may be able to achieve Class A even if operated in a continuous flow mode at temperatures in the 53 to 55°C range. Even if a short batch time of a few hours is required following this digester, this is much better than the 24 hour batch requirement (at 55º C) according to the time/temperature equation. Columbus Water Works is attempting to develop a PFRP Equivalency for this process, and show that it can work for essentially any municipal wastewater sludge. § The concept of coupling a continuous flow thermophilic digestion system with long- term lagoon digestion and continued pathogen destruction to provide a Class A final product would be attractive for the SHDF, given the existing facilities and operation conditions. This approach might need to be implemented through EPA’s Class A Alternative 4, which requires that the final product be proven as Class A through testing for pathogen densities. Alternative 4 is sometimes used when the process does not meet EPA’s stipulated time/temperature requirements for Class A, but other factors are being used to create Class A material.

Digestion Capacity at the SHDF With Thickening With the thickening process outlined in the previous section of this Chapter, the digester feed material would be 5.5 percent solids. Table 6-9 shows year 2025 situation for City-only sludge projection and the full County projection. Peak 2-week sludge projections are estimated and flowrates to digestion shown in Table 6-9. The analysis shows that even with 2 digesters out of service (out of the 8 total digesters), there would be adequate capacity in terms of total Solids Residence Time (SRT) for any type of digestion that might be considered.

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Table 6-9. Future Digester Capacity at the SHDF 2025 2025 Parameter City-Only County Average Sludge Production to the SHDF (pounds solids/day) 118,200 173,300 To Digesters: After Thickeninga Average Annual (lbs/day) 112,300 164,600 Flow to Digesters Average Annual (gallons/day) at 5.5% Solids 245,000 359,000 Peak 2-Week Solidsb (lbs/day) 157,200 230,400 Peak 2-Week Flow (gallons/day) at 5.5% Solids 343,000 502,000 Digester Volume: Four New Digesters Total (gallons) 7,200,000 7,200,000 Four Old Digesters Total (gallons) 5,600,000 5,600,000 Total Digester Volume (gallons) 12,800,000 12,800,000 Total Digestion SRT (days): Average Annual Production with 1 Tank of Each Size Out of Service 39 27 (9.6 million gallons in use) Peak 2-Week Production, All Tanks in Use (12.8 million gallons) 37 25 Peak 2-Week Production, 1 Tank of Each Size Out of Service (9.6 million 28 19 gallons) a At 95 percent capture for thickening. b Peak two-week loading estimated to be 40 percent greater than average annual loading.

Class B Digestion Alternatives at the SHDF Class B mesophilic digestion alternatives are shown with simplified schematics in Figure 6-4. Mesophilic digestion is being accomplished currently with all 8 digesters being operated in parallel configuration. An option shown is to modify the piping so that the digestion system could be operated as a two-stage system. This would help to reduce the sometimes elevated VFA levels in the digesters. A slight improvement in VSR is likely with this two-stage system. Therefore, due to reasonable cost and positive benefits, this modification may be helpful in providing a somewhat more stable digested biosolids material for subsequent processing – i.e., in dewatering, lagooning, or other process. During workshops with Colorado Springs Utilities, it was decided that Class B alternatives were not recommended for consideration as long-term options in this Masterplan. However, off-site Class B slurry application as an interim or emergency measure should be recognized as a short-term alternative.

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Figure 6-4. Class B Digestion Alternatives

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Class A Digestion Alternatives at the SHDF Figure 6-5 shows simplified schematic alternatives to achieve Class A biosolids within digestion systems at the SHDF (digestion includes acid digestion in the Sludge Main, formal digestion reactors, and digestion within FSBs). Table 6-10 shows estimated VSR for each digestion process option. These have been estimated based on sludge characteristics at Colorado Springs Utilities, experience elsewhere, and considering the effects of partial acid digestion within the Sludge Main. As shown, there is some additional VSR expected within the digestion system, particularly for the options that include thermophilic digestion.

Table 6-10. Estimate of VSR for Digestion Alternatives VSR Estimated for 20- to 25-Day Digestion Process Alternative Total SRT Class B: Current Single-Stage Mesophilic 55 2-Stage Mesophilic 56 Class A: 2-Stage Thermophilic With Batch 2nd Stage 57 Temperature-Phased Digestion With Batch Tanks 59 2-Stage Thermophilic Followed By Mixed Thermophilic / Mesophilic 55 Mesophilic Single Stagea 55 a This system is only Class A with long-term FSB pure storage mode. Note: All alternatives operate with acid digestion sludge main.

Definitive Class A Process. The first two alternatives show how definitive Class A digestion processing is achieved entirely within the digestion reactors at the SHDF. These two alternatives include thermophilic digestion at about 55 °C and thermophilic batch operation to meet EPA’s time/temperature equation for Class A process designation. The downside with these two alternatives is that the operation becomes more costly and complex because of batch operation, especially if separate batch tanks are constructed as shown in the second alternative.

Less Than Definitive Class A. The third and fourth Class A alternatives shown in Figure 6-5 provide less than definitive Class A processes. These alternatives would need to use final product pathogen density testing, along with some process monitoring work, to prove that Class A biosolids are being produced. This approach uses EPA’s Class A Alternatives 3 or 4 instead of the definitive time/temperature approach within EPA’s Class A Alternative 1. The advantage of these less- definitive Class A options is that their operation is simpler, in particular the digestion reactors which operate in continuous flow mode.

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Figure 6-5. Class A Digestion Alternatives

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The third Class A alternative is a relatively simple approach to Class A digestion – i.e., raising the temperature to thermophilic operation on the four newer digesters, and repiping to make the four older digesters a second-stage digestion system. This approach would have the least capital cost of any of the Class A options shown and would retain low operating costs for the digestion system. Heating requirements for thermophilic digestion are higher than for mesophilic digestion, but the thickening system greatly reduces the quantity of sludge that must be heated to thermophilic temperatures.

The last Class A alternative uses long-term storage in FSBs to achieve Class A biosolids. Further discussion of this alternative is contained later in this Chapter.

Product Pathogen Testing to Prove Class A. Conducting product pathogen testing to prove that Class A biosolids have been created is an approach being used by several wastewater agencies. Typically, a large pile of biosolids is created from an air drying operation and frequently this pile contains the entire production from a summer season of air drying. However, the “pile” does not have to be dried material. The pile can be lagooned sludge or dewatered cake material, etc. For large operations, at least 12 random and representative samples of biosolids from an annual pile are required (based on “monthly” sampling needs for large plants). The samples are sent to a qualified biosolids pathogen testing laboratory to have the pathogen densities determined – specifically viable helminth ova and enteroviruses - as well as either fecal coliform or salmonellae density. Analytical work takes at least 5 weeks, so that time for sampling and analytical work often encompasses 2 or 3 months.

Once pathogen densities are proven to be within Class A criteria, the pile(s) sampled are declared to contain Class A material. Sometimes, annual air-dried piles are tested for pathogens over the winter months, and the biosolids are then ready to be land applied as Class A material the next season.

There are risks with the product testing approach, but agencies have developed their processes to minimize risks of failing the pathogen tests. For some agencies even if a pile failed its pathogen density tests for Class A, the pile can simply be retained on-site for re-testing a few months later when further pathogen reduction has occurred.

Class A Digestion Option Summary. For Colorado Springs Utilities, the requirement of having a definitive Class A process entirely within the digestion reactors does not seem necessary, since direct dewatering of digested biosolids and transporting off-site for Class A land application would be costly (due to high water content of dewatered biosolids). Also, transporting Class A digested cake off-site for beneficial use in the winter months may be difficult due to soil and/or climatic reasons. Holding Class A biosolids in the FSBs through the winter would seem simpler and would allow destruction of an additional 30+ percent of volatile solids within the FSBs. Then, dredging, dewatering, and possibly air drying can be conducted in warmer seasons. Therefore, the third Class A alternative appears to be an attractive option which uses relatively non-complex operations to achieve Class A biosolids at the SHDF.

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Iron Chloride Addition Iron chloride is currently added far upstream in the wastewater collection system, at the Sand Creek Lift Station. The iron added, however, is useful in controlling the hydrogen sulfide in the digester gas at the SHDF. The air permit for the SHDF requires limiting sulfur oxide emissions from the digester gas so that controlled iron addition is needed to maintain emissions below permit levels.

Another use of iron chloride is to precipitate phosphate from solution and thus minimize the production of struvite within digesters. However, normally, iron will react with both sulfide and phosphate, and has some preference for sulfide. Therefore, to have an impact in reducing the phosphate concentration in the digesters, more sulfide will probably be precipitated as well. Thus, the iron chloride dose could rise significantly to achieve major phosphate reduction within the digesters.

Adding iron chloride directly at the SHDF digestion complex is possible, however, iron should not be added anywhere near where the sludge is being heated. Therefore, iron should not be added to the raw sludge being transported through a heat exchanger. Iron chloride can be added directly to each digester; however, this requires multiple feedpoints typically through the sidewall of digesters.

Iron chloride can also be added at the BSPS wet well at the Las Vegas Street WWTP. This would be a relatively easy chemical addition point and would be helpful in keeping sulfide levels controlled within the Sludge Main.

Post-Digestion Storage Following digestion, the sludge is currently pumped to the FSBs and there is no need for digested sludge storage tanks. If dewatering is conducted directly after digestion reactors, there will be a need to separate the digestion process from the dewatering operation through the use of a storage tank that could accept sludge from all digestion reactions being operated, and provide a mixed/blended feed to the dewatering equipment. Providing this blended feedstock to dewatering equipment is important, since shifting feed from one digester to another typically means adjustments in polymer dose and perhaps machine operation to provide the most cost-efficient dewatering.

Digester Improvements During the 1998 Expansion Project, four additional digesters were constructed. During the preliminary design, digester cover and mixing alternatives were evaluated. Submerged-fixed covers and mechanical draft tube mixers were the selected options. The following describes the existing covers and mixing equipment and the recommended systems associated with the newer units.

Floating Covers. The four original digesters (existing prior to the 1998 expansion) at the SHDF have floating covers. Floating covers are ballasted to balance the buoyant forces of the digester fluid, the cover weight, and the gas dome pressure. The floating cover is designed to maintain the liquid surface within the dome and to hold the digester gas pressure within a desired operating range. By keeping the digester liquid surface up in the dome, the liquid/gas interface area is kept to a

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minimum, and foam is constrained within this relatively small surface area. However, foam can escape around the perimeter of the floating digester cover.

From an operational standpoint, the existing floating covers work well, however plant staff periodically enter the interior of the digester cover (confined space) to pump out 8 to 10 inches of water that condenses and pools between the main truss members. If a significant unbalanced volume of water is collected on one side of the cover, the cover could be jammed into its guides, or possibly could be upended and submerged into the digester itself.

Another concern with the existing digester operation is the fugitive emissions of the digester gas. In order for the digester to float freely, a gap must exist between the tank wall and the cover. This gap contains digester liquid through which gas escapes to the atmosphere. The gas has relatively high concentrations of H2S which could have an impact on the site’s air permit.

Submerged-Fixed Digester Covers. As stated above, during the 1998 expansion project, four additional digesters were constructed with submerged-fixed digester covers. Submerged-fixed digester covers are structurally fixed to the wall of the digester tank. The cover and the center gas dome project above the top of wall elevation such that the liquid level in the digester is above the top of the wall. These covers are operated so that the liquid surface is maintained within the gas dome to minimize the liquid/gas interface.

The optimal method of operation for a digester with a submerged-fixed cover is to maintain a continuous feed and withdrawal of sludge. Using continuously operating pumps to feed sludge to the digesters, digester liquid is displaced into the gas dome withdrawal weir and overflow system. A continuous feed and withdrawal system is ideal since it eliminates abrupt changes in flow rate and organic loading that could produce shock loading effects. These shock loads can result in fluctuations in gas production, gas quality, pH, alkalinity, organism growth rate, total volatile acid concentrations, and other operating parameters.

The small liquid/gas interface area facilitates scum and foam control. Foam control methods consist of pumped spray water which covers the liquid surface inside the dome. Floating scum and foam residue is automatically withdrawn from the liquid surface of the digester dome.

An emergency overflow weir and discharge pipe are also provided in the dome as a safeguard to prevent overfilling or pressurizing the digester. Overfilling or pressuring the digester could cause structural problems. The cover is fixed into the walls of the digester for reinforcement and also has the weight required to overcome the buoyant forces exerted by the digester contents and gas pressure. This emergency overflow capability, because it is so critical, is designed to always be in service.

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Foam cannot escape from the digester with a submerged-fixed cover. Therefore, it is recommended that a high volume circulation pump be installed to spray down the foam in the digester gas dome at the liquid/gas interface. Maintenance requirements are reduced because washing down covers will not be necessary. Also, the solid cover eliminates condensate pumping problems. No annular space is available for digester gas to escape to the atmosphere.

When comparing the available volume with floating covers and the submerged-fixed covers, it can be shown that a submerged fixed cover could provide an additional 25-percent volume over the floating cover digester. This is due to the freeboard requirements of a floating cover which is converted to usable volume with a submerged-fixed cover.

This increase in volume proportionally improves the detention time of the digesters. A 25 percent increase in detention time is a significant advantage that will also improve the digestion process.

Submerged-fixed digester covers are recommended for replacement for the existing original four digesters because it provides the following:

§ Increased usable volume by 25 percent over existing floating cover tanks. This equates to a 25 percent increase in digester detention time as well. § Lower maintenance requirement by eliminating foaming on the digester roof and condensation build-up in the digester cover. § Fugitive digester gas emissions can be eliminated because there is no annular space between the digester cover and the tank walls. § In the future, the gas pressure can be increased to improve the boiler operation. § Provides consistency with 4 newer units.

Digester Mixing Unconfined gas lance and mechanical draft tube mixing are described below.

Unconfined Gas Lances. Unconfined gas lances are the current form of mixing in the four original digesters at the SHDF. Operation of this system involves compressing a portion of the digester gas that is produced and discharging it through the lances below the liquid surface in the digesters. There are 12 lances spaced evenly around the digester at a distance approximately two thirds from the center of the tank. Lances are long tubes with multiple orifices at the ends which diffuse the compressed gas into the digester liquid. As the gas rises, the fluid is displaced to mix the contents. These lance systems can operate in both fixed and floating covers. With a floating cover, the lances influence different levels in the digester as the cover travels up and down with the varying level in the digester. This system was designed primarily as a scum mixing system, not as a complete mixing system.

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Periodically, there have been incidents of foaming in the digesters. Operations staff say that this is directly correlated with foam events at the Las Vegas Street WWTP. One other possibility is that the foaming may result because of accumulation of nutrients in the digesters. This may be why the compressors can only be run at a lower speed, because if more gas was pumped (more mixing and better distribution of food), the foaming could be aggravated.

Another item of consideration with the gas lance systems is the fire code. Currently, the code that most affects the Clear Spring Ranch digester facility is the National Fire Protection Association, NFPA, 820, Fire Protection for Wastewater Treatment and Collection Facilities. This code governs the area classification of the facilities which could impact the location of gas handling equipment and ventilation characteristics of the facilities.

Mechanical Draft Tube Mixers. Mechanical Draft Tube Mixers (MDTM) are designed with a radial impeller inside a vertical pipe, or draft tube. The mixers are designed to operate either in a upward or downward mode, and are arranged in a configuration so that they can provide a variety of mixing patterns. MDTMs are provided for the four mixed cover digesters at the SHDF.

MDTMs provide a locally higher velocity gradient, whereas unconfined lances distribute the gas mixing energy proportional to their physical spacing. With the draft tube mixers, sludge can circulate from the bottom of the digester tank better than with the unconfined lance system. This system is designed to be a complete mix system.

Since the mechanical equipment can be withdrawn from the top in the fixed cover digesters, the digester can remain in service while maintenance is being performed on the mixers. Each mixer can be pulled from its location for maintenance without letting gas escape from the digester. This is possible because of a gas isolation sleeve that is always submerged below the liquid level to provide the seal.

In practice, the MDTMs have proven to be very reliable, and the capability to control operation of the mixers with the SCADA system gives flexibility of operation.

There has been some speculation by operations staff because there appears to be more struvite in the new digesters than in the old, that the mixing system contributes in some way to additional struvite buildup. Further investigation is warranted to identify the causes and remedies for the struvite problem.

Conversion of the four existing digester covers to submerged-fixed type and from an unconfined gas lance system to a mechanical draft tube mixing system is recommended in the future depending on equipment condition to prevent the floating covers from causing problems as they age. The primary reasons to install submerged-fixed covers are:

§ Foam control § Automated mixing control § Reliability

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FSB Options/Improvements The FBSs are long-term storage and treatment units that contain digested wastewater solids typically for two to three years average before the harvested biosolids are removed and injected into the DLD. Because of the application frequency and lagoon feeding schedule, some solids are held only for a couple of months before dredging, while the bulk of material is held for longer detention times.

The main functions of the FSBs are:

§ Achieve volatile solids reduction by long-term stabilization of solids through continued anaerobic digestion. § Destroy maximum amount of solids so that less solids are dredged and disposed to the DLD areas or dredged and beneficially used. § To provide further pathogen reduction. As discussed below, there are ways to achieve Class A biosolids with lagooning. § To provide storage particularly over the winter months when DLD operations or beneficial use of solids is difficult or impossible to undertake. Dredging is also difficult in the coldest months. § FSBs consolidate and thicken solids to over 5 percent, allowing dredging to be conducted cost-effectively.

Before the 1998 expansion, there were six FSBs at the SHDF. Three new FSBs were constructed as part of the 1998 expansion. All FSBs operate in parallel. The FSBs are 15-foot liquid depth basins with a surface area of 5 acres each (45 acres total). Construction costs for the three new FSBs was approximately $2,100,000 in 1998. We anticipated regulators will require impermeable lining for new FSBs, therefore construction costs for additional FSBs are estimated to be higher.

Additional FSBs Modifying or improving the existing system as well as expanding existing system capacity to accommodate future growth and loadings at the SHDF is evaluated as part of this Masterplan. Table 6-11 describes the projected FSB loading rate based on the two population sources and design loading of 20 lbs VS/1,000 sq ft./day. The loadings below assume 55 percent VSR is achieved within the anaerobic digestion reactors at the SHDF. For some alternatives evaluated, VSR is somewhat higher in the digesters, and, therefore, fewer FSBs are required in the future.

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Table 6-11. Projected FSB Loading Rate Load, lb VSS/1,000 sq. ft./day 2 3 4 5 6 7 Population Additional Additional Additional Additional Additional Additional Source Year Units Units Units Units Units Units Colorado 2005 15.1 13.7 12.6 11.6 10.8 10.1 Springs 2010 16.2 14.7 13.5 12.5 11.6 10.8 2015 17.3 15.7 14.4 13.3 12.4 11.6 2020 18.4 16.8 15.4 14.2 13.2 12.3 2025 19.5 17.8 16.3 15.0 14.0 13.0 El Paso 2005 21.9 19.9 18.2 16.8 15.6 14.6 County 2010 23.5 21.4 19.6 18.1 16.8 15.7 2015 253 23.0 21.0 19.4 18.0 16.8 2020 27.0 24.5 22.5 20.7 19.3 18.0 2025 28.7 26.1 23.9 22.0 20.5 19.1

As revealed in the FSB loading analysis described in Table 6-11, in order to remain under the design FSB loading rate of 20 lbs. VS / 1,000 ft2 / day, two additional FSBs are recommended to accommodate the 2025 projected loading based on the Colorado Springs projected loadings (10 FBSs in service, 1 FSB being dredged). Seven additional FSBs are recommended to provide adequate capacity based on El Paso County 2025 projected loading (15 FSBs in service, 1 being dredged).

FSB Feeding/Loading of FSBs Previous work with facultative solids basins and lagoons shows that daily feeding is best to maintain the best health of the anaerobic activity within the lagoon. Multiple feedpoints work well to help distribute the solids throughout the basin. However, buildup of material around the feedpoints is a major issue with any feeding of lagoon/basin systems and there has been no low-cost solution to solve this problem. Some agencies have used simpler approaches such as feeding solids lagoons from the side, but this distributes solids less evenly than feedpoints in the basin bottom, and does not appear attractive.

A major issue at the SHDF would be whether the FSB loading rate could be increased. The 20 pounds VS/1,000 sq ft/day loading rate (annual average), is based on extensive work at the Sacramento Regional WWTP in full-scale testing in the late 1970s. The loading rate has been confirmed to some extent for Sacramento over the years when they have exceeded this rate, and began to encounter the beginnings of odor problems in the downwind areas. However, the Sacramento site encompasses 20 lagoons covering 125 surface acres, and there is commercial development within about 2,000 feet of the basins, and residential development within about 3,000 to 4,000 feet. Interstate 5 runs less than 1,500 feet from several of the basins. Therefore, the odor situation is much more severe at Sacramento than at the SHDF. The Sacramento site also utilizes

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12-foot high barrier walls for vertical air dispersion and wind machines which are turned on under certain low-wind, inversion conditions to supplement atmospheric mixing to minimize chances of downwind odors.

Therefore, perhaps at the SHDF, with its more remote location, increased loading of FSBs could be tolerated. This is something that would need to be tested over time to determine what loading rate can be accommodated, but there is a fairly good chance that the loading rate could be boosted to 25 lb VS/1,000 sq ft/day. When the loading rate becomes too high, the aerobic water cap layer will start to lose its odor treatment capability, and stronger odors will break through the basin cap layer and be emitted to the atmosphere. So, preserving the aerobic cap layer is the crucial element for FSB odor control. The brush aerators are important in this function in that they insure little debris or scum is on the surface which would inhibit natural aeration of the surface water through wind action. Most reaeration of surface cap water is accomplished through wind action, not through aeration by the brush aerators. If odor emissions from the surface of the FSBs started to become an issue with higher loading rates, there is the possibility of adding barrier walls to achieve greater vertical dispersion and atmospheric mixing to dilute the odors, similar to the situation at Sacramento.

If higher loading rates are used, then the FSBs will fill up somewhat faster with solids, and would need to be dredged more often. Currently, the FSBs are on approximately a 3 to 5 year dredging schedule (i.e., dredge two FSBs every year.) For instance, if a 25 percent higher feedrate is used (25 lbs versus 20 lbs), then Colorado Springs Utilities may need to change to a 3-year dredging schedule. This is not expected to be a problem, but a somewhat more frequent dredging schedule may reduce slightly the VSR achieved within the FSBs. Currently, data indicates that about 34 percent VSR is achieved within the FSBs, over the course of the 2 to 3 year average storage time within the FSBs. Most of the VSR is achieved in the first year, with reduced destruction each year thereafter.

Solids Destruction Within FSBs There are no known methods of achieving greater VSR within these facultative basins. The long- term anaerobic biological activity is largely dependent on solids temperature, and this is controlled in the FSBs essentially by ground temperatures, and to a lesser extent by air temperatures. The 34 percent additional VSR achieved in the FSBs is highly relevant in destroying solids so that less solids need to be dredged and processed for final use/disposal. At current production levels, solids destruction within the FSBs is about 2,100 tons/year (dry weight). A typical costs to further process these solids ($200 to $300 per dry ton), this represents an annual cost savings to Colorado Springs Utilities in the range of $0.5 million per year. Therefore, the FSBs are a cost-effective system for Colorado Springs Utilities.

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FSB Inventory and Management Other agencies with facultative sludge lagoon/basins systems have developed procedures for keeping track to some extent of the amount of solids within each basin. This is important for various operational reasons including: (1) need to know if the basin is full – overfilling the basin creates odors, and difficulty in floating the dredge; (2) need to plan for future dredging operations, to insure that too many basins do not reach “full” status during the same year; (3) need to monitor the thickness of sludge within basins to confirm basin health and inventory status; and (4) determine if dredging activity has removed planned quantity of solids.

Sacramento has been using an extensive annual inventory sampling the past two years, whereby about 2,000 samples were collected from the 20 lagoons. Thirteen specific locations were selected in each lagoon (7-acre size each) to get adequate coverage, and samples at 7 different depths are collected at each location with special devices to collect proper samples of sludge at each depth. Sampling crew includes 2 people in a boat. Temporary staff are hired in the summer for this program. By taking these data, Sacramento has developed an operating model of solids inventory in each lagoon. This model is now more accurate since the plant has implemented computer- controlled loading of each basin, through loading calculations, and changing the automated basin feed valves. Sacramento staff are using the model to predict how their total inventory is changing, and insuring that excessive inventory is not building up in the lagoons. They are also planning ahead on dredging activity for the next season. Finally, the data shows how thick the solids are in each basin, insuring that dredges have sufficiently thick material to conduct cost-effective dredging.

Everett, Washington and City of Portland Oregon also collect solids inventory data from their lagoons for many of the same purposes and reasons described above for the Sacramento system. An improved inventory management system at the SHDF would help operating staff make better decisions and be able to operate the system more effectively. Flow measurement should not be a problem if number of tank loads is recorded.

Dredging FSBs There is substantial difficulty obtaining good data on dredging flowrates and obtaining valid samples from dredged material to determine what is being removed from the FSBs. Flowmeters on dredges are difficult to keep accurate due to vibration and the nature of the operation. Since dredged material characteristics change minute by minute, it is difficult to determine the average of what has been removed over the course of a day. Other agencies have developed procedures to take fairly frequent grab samples of dredged material so they can develop a reasonable composite for each day’s dredging activity. This has helped in getting more accurate information. Sacramento has implemented ground-based flowmeters on the dredge pipelines to obtain better flow measurements. At the SHDF, with the use of vehicles for harvested sludge injection into the soils, the capacities of the vehicles are known, so that daily quantities injected (gallons) may be calculated. In general, an improved system of data from dredging operations is likely to be helpful at the SHDF. Required thickness of dredged material may be different depending on whether harvested material needs to be injected with TerraGators, dewatering is used for subsequent processing. However, in general, dredging such solids to obtain more than about 5 percent dry matter concentration on an average

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basis is expected to be difficult. Dredge operators may be able to refine their operational procedures to achieve thicker material, if downstream processing benefits from thicker material.

With larger numbers of FSBs in the future and with greater solids production, it is likely that another dredge system will be needed. The existing dredge was purchased in 1999. It is assumed that for the City projections, the existing dredge will need to be rehabbed at some point during the planning period. For County projections, a new dredge and rehab of existing dredge is assumed.

Long-term FSB Storage for Class A Biosolids To achieve Class A biosolids within lagoons that are fed anaerobically digested sludge, long-term storage is needed without any new/fresh feed material. This Class A storage period is termed “pure storage” in order to differentiate it from any storage operation that receives sludge input of any kind. The length of time required to achieve Class A biosolids within “pure storage”, after a lagoon has been fed for about 4 years of digested material, is subject to debate in the industry. Chicago’s has received site-specific PFRP Equivalency from EPA for a system that has the following process train: mesophilic anaerobic digestion, followed by lagoon filling (about 1 year to fill lagoon), followed by 1.5 years of “pure storage”, followed by summertime air drying to about 60 percent solids. The time period in pure storage is somewhat a function of climate and temperature. At the San Jose, California plant, their solids system has had adequate capacity to achieve 2 years of “pure storage” in a system that has the following process train: mesophilic anaerobic digestion, followed by 1 to 2 years to fill a set of lagoons, then 2 years in lagoon “pure storage” mode, then summertime air drying to 75 percent solids. All solids for each of the past 6 years at San Jose have been placed into an annual pile, then the pile is sampled for pathogens, and proven to satisfy Class A pathogen density criteria.

A WERF study has included evaluation of this concept (Class A Biosolids Through Storage and Air Drying – Perry Schafer of Brown and Caldwell is Principal Investigator). This study is expected to have a final report in 2004. However, there will be no definitive criteria established in the report for this type of Class A processing since the “pure storage” time requirement depends on local temperature and other factors that have not been adequately defined. Research on this approach at Tulane University in the 1980s suggested that about 1.5 years within the pure storage mode should be adequate for pathogen reductions in climate similar to New Orleans.

Considering the climate and situation at the SHDF, we believe the best estimate for “pure storage” mode following 4 years of FSB feeding, is probably in the 1.5 to 2.0 year time-frame. Therefore, our analysis here assumes 2 years, to be safe. Several additional FSBs are required for this type of operation, since after each lagoon reaches the point of being full, it is set aside in pure storage for a 2-year period. Procedures would need to be established that preclude digested sludge from being fed to any lagoon that is in this pure storage mode. Following the stipulated time, dredging of the lagoon is conducted, and the sludge is processed to its final form. Sampling and analysis of the final product is required to prove it meets Class A pathogen standards. Table 6-12 indicates the number of additional FSBs required:

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Table 6-12. Additional FSBs Required for Current System Operation and Class A “2-year Pure Storage” Operation FSBs 2025 City-Only 2025 County

No. of FSBs required for current System operation 11 16

No. of additional FSBs required For 2-year Pure Storage operation 5 8

Total number of FSBs required 16 24

The additional number of FSBs is highly significant since there is difficulty finding space for additional basins and constructing and operating the additional FSBs is costly. We believe this approach is not as feasible as the alternate approach for Class A biosolids defined within the digestion section included in this Chapter. The alternate approach uses thermophilic digestion to achieve Class A pathogen kill. And later in this Chapter, another method of Class A processing is defined – heat drying of biosolids.

Additional Solids Testing Representative samples of harvested (dredged) solids should be tested for percent solids, percent volatile solids, TKN, Ammonia-N, Nitrate N, Total Phosphorus, and all Part 503 metals (As, Cd, Cu, Hg, Pb, Ni, Mo, Se, Zn). The purpose is to assess potential for future off-site application to agricultural land. Existing data should be evaluated fully before beginning this work. Additional testing should be conducted along with other routine sampling and testing required under the current permit.

DLD Options/Improvements

Options to Control Groundwater Beneath DLDs There has been concern expressed by the Colorado Springs Utilities Staff that use of six unlined FSBs and the unlined DLDs will result in a buildup of groundwater with elevated metal and/or salt levels.

FSBs typically do not leak due to biological sealing of soil pores and compaction from the water column; this should continue to be monitored with simple piezometers or shallow monitoring wells immediately adjacent to the FSBs. It is also possible to perform a leak test on a representative FSB to quantify seepage losses. There may be seepage from the FSBs but the question is whether losses are significant and impacting site operation or ground water quality. This question has not been fully addressed.

DLD units may generate some percolation loss as a result of hydraulic load applied outside the peak evaporation season. However, it may be possible to eliminate such losses by shifting to a more seasonal operation and providing interim tillage to maximize evaporation. Experience in

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Sacramento has demonstrated that the objective of DLD operation should not be to achieve percolation loss. Operators have ceased deep ripping and focused on shallow tillage to turn the soil between injection cycles. Tillage reduces subsoil permeability through compaction, and re-exposes the soil to promote drying. Recommendations follow below.

In addition to reducing percolation losses, it may be possible to control ground water levels by providing agricultural drain tile. DLD units which are at risk of violating the 5-foot separation distance requirement for ground water should be identified. It may be feasible to provide shallow (i.e. 6 foot depth) tile with gravity outlets to the retention basin. Tile installation would typically consist of perforated pipe with a 60-70 foot spacing.

A number of monitoring wells on the site show that there is migration of water with elevated salt levels down gradient from the DLDs and FSBs. Chapter 9 addresses the salt balance and water balance on the site further.

DLD Improvements and Equipment Modifications Regardless of groundwater depth, DLD operation is clearly limited at times due to wet soils and trafficability for application vehicles. There are several possible ways to address this problem. Based on experience in Sacramento, DLDs are best operated on a seasonal basis to maximize evaporation potential. Solids are stored in FSBs during the winter, then applied to the DLD units from about April through October. Applications are made approximately weekly during the season. Each application is approximately 1.0 to 1.5 inches of material at a solids concentration of about 4 percent. Between applications, DLD soils are plowed once and disked 2-3 times to promote evaporation. In this manner, up to about 150 dry tons are applied to each acre on an annual basis at Sacramento.

The climate near Colorado Springs should be evaluated to determine evaporation potential, and interim tillage should be considered. The goal of this operating strategy is to promote evaporation rather than infiltration. Rocks in the soil at Clear Spring Ranch may limit tillage potential. Testing should be performed to determine appropriate tillage schedule and determine target increased evaporation rates. Disks and plows may not be compatible with rocky areas; some type of shallow subsoiler may work better.

A second possibility is to increase the number of DLD units and continue the present operating strategy. If land is available for this purpose, expanding the DLD operational area would be logical. We understand that an additional 36 acres are being added to the system in 2004. According to the information included in the Preliminary Report-Clear Spring Ranch Excess Water Study (January 15, 2002), an additional 203 acres (includes the 36 acres to be added in 2004) has been identified as “future DLD” or “DLD Expansion”. However, if FSB expansion is recommended, this future area may need to be reduced.

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The entire DLD system at Clear Spring Ranch presently totals approximately 194 acres with an additional 15 acres for grit and screening waste disposal. The following is a summary of the DLD areas at Clear Spring Ranch and associated acreage. Information was obtained from the Preliminary Report Clear Spring Ranch Excess Water Study (January 15, 2002).

§ North DLD: 26.73 acres § East DLD: 40.79 acres § West DLD: 19.88 acres § South DLD: 43.59 acres § Southeast DLD: 62.91 acres § Grit Disposal: 14.32 acres

Third, solids could be dewatered or air-dried prior to application. There is expense associated with either approach and different spreader equipment would be required. However hours spent running TerraGators in the present configuration would be drastically reduced.

Finally, a portion of solids could be hauled off-site for land application on agricultural land. The simplest approach would be if solids continued to be managed as slurry. This could be a contract operation, supplementing the current DLD system. Partial dewatering or air-drying would increase flexibility and options. Drier material could be composted, for example, or disposed in a landfill depending on cost issues.

Current and Future DLD Capacity A key for determining the need for expansion or modification of the current facility is understanding the solids balance and current biosolids application rates. It has been estimated that the current hydraulic application to DLD units through injection is approximately 7 inches per year. Since trafficability is limited at times, there is an implication that the DLD units are at capacity. The Sacramento operation achieves an application between 30 and 40 inches of liquid during April to October. However, evaporation rates are greater and soils have better characteristics (level, no rock) for tillage at Sacramento.

The best way to define capacity is to isolate one representative DLD unit (or a portion of a DLD) and begin a more systematic operation. This would include running the TerraGator at constant speed and known discharge rate to achieve a 1-inch application, for instance. An agricultural wheel tractor (approx. 100 hp) should be rented or purchased along with a heavy plow and construction disk. If purchased, equipment should be pre-owned to minimize investment until it is clear what works best. For example, rocks that are common in DLD soils will interfere with operation of some tillage implements.

Operational experience will then define limits for DLD operation. If one inch/week of liquid application is satisfactory, additional loading should be tested. The Sacramento model for interim tillage should be tested. Maintain a record of applications with comments regarding success or problems. Results will allow refinement of site capacity projections.

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Required capacities based on solids quantity projections are listed in Table 6-13 below. In order to meet the current hydraulic application of 7 inches per year in the future, additional DLD acreage is required. Based on current DLD acreage of 194 acres, injection rates based on Colorado Springs projections and El Paso County in 2025 are approaching 10 inches/year and 15 inches/year, respectively (based on 4 percent solids).

As mentioned previously, an additional 203 acres (includes the 36 acres to be added in 2004) has been identified as “future DLD” or “DLD Expansion”. However, if additional processes are recommended such as additional FSBs, thickening, dewatering, and drying operations, this future area will be reduced, therefore 100 additional acres was assumed. As shown in Table 6-13, DLD loading based on an additional 100 acres would remain under 7 inches/year (at 4%) for the 2025 based-Colorado Springs projections and through approximately 2005 for the County based projections.

Table 6-13 also displays the DLD acreage required for the loading to remain under 7 inches per year for both population based scenarios. An additional 226 acres of DLD would be required to remain under 7 inches/year for the El Paso County projections. However, feasibility of potential new DLD units needs confirmation (i.e., slope, etc). Dewatering could be a method of operation to reduce the future DLD area required.

Table 6-13. Projected DLD Loading based on Additional Acreage Projected DLD loading based on 294 acres DLD loading based on 420 acres Loading (100 additional acres) (additional 226 Acres) Population Year DT/yr DT/ac/yr inches/year @4% DT/ac/yr inches/yr @4% 2005 6951 24 5.22 17 3.65 2010 7455 25 5.60 18 3.92 City of Colorado Springs 2015 7970 27 5.98 19 4.19 2020 8481 29 6.37 20 4.46 2025 8991 31 6.75 21 4.73 2005 10061 34 7.56 24 5.29 2010 10833 37 8.14 26 5.69 El Paso County 2015 11620 40 8.73 28 6.11 2020 12402 42 9.31 30 6.52 2025 13184 45 9.90 31 6.93

Site Monitoring and Testing To provide an assessment of DLD soil characteristics and trends, it is recommended that a soil sampling and testing program be implemented. An application log should be developed showing the volume of solids applied to each DLD unit on a daily basis. Data should be entered into a spreadsheet to allow easy compilation and evaluation. A minimum of three representative DLD

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units should be sampled to a 12-inch depth. Composite samples for a DLD unit should be collected using an agricultural soil probe which costs approximately $200. Individual cores (12-20 per DLD unit, collected in a random pattern) should be placed in a clean plastic bucket and mixed thoroughly. A subsample is then placed in a 1-quart ziplock bag to send to the lab. Minimum analysis should include pH, salinity, and organic matter content. It is also recommended to determine baseline TKN and Part 503 metals (As, Cd, Cu, Ni, Hg, Mo, Pb, Se, Zn). Trends in pH and salinity are of particular interest to ensure a favorable environment for soil microorganisms which decompose solids in the DLD system.

Dewatering This section includes a discussion of processes and equipment used for dewatering of raw or digested sludge. Dewatering reduces the moisture content of digested sludge so that it has a semi- solid consistency ranging from 15 percent to 40 percent dry solids. Sludge dewatering reduces hauling costs and disposal costs related to volume. It also is a prerequisite of many post-treatment processes. The following describes potential options for sludge dewatering at the SHDF.

§ Dewatered cake applied to DLD (this modified DLD system would provide additional DLD capacity) § Land application of dewatered and heat dried product for marketing and distribution § Land application of dewatered and air dried sludge § Dewatered sludge for hauling to a landfill on an emergency basis § Dewatered sludge fed to the RFBB for fuel

Potential long-term dewatering system improvements for the SHDF are reviewed in this section. The following four dewatering and two combination dewatering/drying technologies were identified:

§ Belt Filter Press (BFP) § Centrifuge § Fournier Rotary Press § FKC Screw Press

Dewatering/Drying Equipment:

§ Centridry™ § J-Vap Dewatering/Drying System

The analysis of each technology is described below. Preliminary screening of the various technologies indicated that the rotary press and screw press as well as the two dewatering/drying technologies were not well suited for application at the SHDF. Based on past experience, the capital and operating costs for centrifuges and belt presses are close enough that for a planning study, they

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are the same. Because centrifuge dewatering best fits Colorado Springs Utilities concept for unmanned operation and is better for odor control, the dewatering cost estimates in this report are based on centrifuges. However, if the biosolids are air-dried, belt presses may be referred for odor emissions reasons at the drying beds. As each project is considered, the final choice between the two technologies should be done in preliminary design, with the operations staff’s participation.

Belt Filter Presses Belt filter presses were originally developed for the pulp and paper industry and have been used to dewater wastewater sludges since the early 1970s. The following paragraphs describe the process and its performance, control, and maintenance.

Belt filter presses consist of two or three fabric belts that rotate around and through a series of rollers. The sludge is applied to the belt and passes through three zones as it is dewatered: gravity, compression and pressure.

In the gravity zone, water drains from the sludge or is drawn by the capillary suction forces exerted by the pores of the belt fabric. Plows mix and turn the sludge to enhance dewatering. From the gravity zone, the sludge enters a compression zone. Here the sludge is squeezed between two belts, an upper and a lower. These two belts begin about an inch apart and gradually converge to the point where the two belts begin to exert mechanical pressure on the sludge cake. From this transition point to the cake discharge point, the sludge is in the pressure zone. In this zone, the two belts pass around a series of rollers, which vary in size and offset. As the belts and sludge travel this serpentine path, the cake is exposed to increasing pressure, about 350 kPa by the end of the pressure zone.

Before sludge is applied to the belt filter press, the sludge must be macerated and conditioned. Maceration reduces the size of coarse sludge solids so that they do not cause stress concentrations in the belt, which can lead to shorter belt life.

Polymer conditioning is required to flocculate the sludge particles so that they drain and compact well. Polymer is added upstream of the press and allowed to flocculate in a small chamber prior to distribution over the belt. Although injection of the polymer directly upstream of the flocculation chamber is most common, it is good practice to provide several injection points so that longer reaction times can be achieved in the sludge feed pipe if that is found to be beneficial.

Water expelled from the sludge through each of the zones drains from the belt and is collected by a series of trays. In addition to this expelled water, a strong water spray is used to wash the belts on their return from the end of the dewatering zones. This spray dislodges fines from the belt fabric pores so that dewatering is not impeded in the next service cycle. This wash water also is collected by the trays and conveyed from the machine. A curb 8 to 16 inches high surrounds the entire belt filter press, the enclosed floor sloping to one or two floor drains. The expelled water and wastewater discharge to this floor space. Any drip or splash that falls from the belt filter press is also captured within the curbed area.

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Process Performance. Belt filter presses typically dewater anaerobically digested, mixed primary and secondary sludges to between 16 and 22 percent dry solids. Denser cakes generally are associated with a greater proportion of primary sludge.

A recent sampling program (2003) was undertaken at the Laguna Subregional Wastewater Treatment Plant in Santa Rosa, California (Laguna) as a preliminary screening method to determine potential performance for different dewatering technologies. Laguna’s current daily influent sludge flowrate averages 146,000 gpd at 2.7 percent solids by weight (Clear Spring Ranch is currently (2002) receiving influent sludge flow of 334,000 gpd at 3.1 percent solids by weight).

Laguna has a typical total sludge feed rate to all existing belt presses of 285 gpm based on 10 hrs/day, 6 days/week operation. Actual feedrate to each press varies according to the number of presses in operation and availability of trucks to receive filter cake. The dewatering throughput ramps up and down at various points through the day depending on truck availability. Filter cake solids average for the previous five years of operation is 15.1 percent by weight, with monthly averages ranging from 13.7 percent to 16.6 percent. A recent 24 hour operation trial to evaluate reduced loading rates reportedly produced a sludge cake with 17 percent solids. The facility produces a daily average of 14.3 dry tons/day, with a monthly range of 9.9 to 21.4 dry tons/day. This performance is typical for digested sludge.

Laguna Subregional staff collected a 2-gallon sample of anaerobically digested sludge and forwarded the sample along with 1 pint of the current polymer used for dewatering. The testing indicated that the test sample could not be dewatered in the lab to greater than 14 percent. Analysis of the dewatered sludge revealed that all free water had been removed from the sludge cake and that the remaining water was contained within the cell wall of the sludge particles.

Solids capture generally ranges from 90 to 98 percent, with values in the high end of the range more common. Capture depends on the digested sludge particle size distribution and upon the effectiveness of the polymer. The polymer dosage would be expected to range from 10 to 20 lbs/ton of dry solids.

Operation and Process Control. Automation of belt filter press dewatering has not been achieved with any degree of success. There is minimal measurable feedback that allows process optimization. Some efforts have been made to measure the capillary suction time and control the polymer dosage accordingly. However, the instrumentation required for this is expensive and has not gained wide acceptance.

Even with the nominal automatic control available with belt filter presses, relatively consistent operation can be obtained. The major concern is fluctuations in feedstock quality. If upstream operations result in variations in the sludge quality, belt filter press operation can quickly go awry. However, if the upstream process is digestion, it is anticipated that the relatively large inventory of digested sludge will dampen short-term quality variations and thus reduce the potential for process upset.

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Maintenance. Belt filter presses are slow moving and do not require precision tooling. However, there are many moving parts that require frequent lubrication, bearing replacement, etc. The major long-term maintenance item is belt replacement. Belts wear or rip and must be replaced at frequent intervals, often two or three times per year. Belt replacement takes a minimum of 4 to 8 hours for two workers. This time period is contingent on providing design details that ensure ease of replacement.

Specifying corrosion and abrasion resistant materials also reduces maintenance efforts. Because of the high humidity environment and the presence of reduced sulfur compounds, corrosion can be a problem. Appropriate materials and finishes are required to ensure premature deterioration does not occur. The finishes must be maintained over the long term to minimize potential corrosion problems.

Ancillaries. Many belt filter press systems use hydraulic power packs to drive the equipment. Electric drives also may be used, in which case compressed air often is used for belt tensioning and alignment.

The most important ancillary service, however, is washwater. About 50 gpm per meter of belt width is used. In addition, an extra degree of reliability has to be built into the system. Belt filter press dewatering will halt if the flow of washwater is disrupted.

Operator Environment and Odor Control. The exposed sludge face and the washwater spray will create a humid, odorous operating environment. Relatively high ventilation rates (likely about 15 air changes/hour) will be required to control humidity and odors in a belt press room.

The exhaust from a BFP dewatering area will have to be treated to remove odors. Most of the costs of air treatment are associated with the volumetric flow rather than the contaminant loading. The high ventilation rates will, together with the need to treat the exhaust air, result in relatively high costs.

Some success has been achieved by enclosing the press in a small enclosure, which isolates the foul air source and limits the amount of air necessary to collect the odorous vapors. The disadvantage of the enclosures is during maintenance on the presses, when the enclosure must be partially dismantled.

Summary. Belt filter presses are expected to dewater anaerobically digested, mixed primary/ secondary sludge to 16 to 20 percent dry solids with a polymer dose of about 15 lbs/ton. There is little control available other than modulating the polymer dosage. Most control decisions are based on subjective evaluation of operation. Maintenance is simple but time consuming due to the large number of moving parts. There are several ancillary services necessary for belt filter press operation, one of the most important being the washwater required. Concerns with belt filter press dewatering include the high humidity environment and the possible emission of odors. High ventilation rates

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will be required to minimize any subsequent problems and this, coupled with the need to provide odor control, could result in relatively high air handling costs.

Advantages and disadvantages of belt filter presses and operational issues are presented in Table 6-14 and Table 6-15, respectively.

Table 6-14. Summary of Advantages/Disadvantages for Belt Presses Advantages Disadvantages § High solids capture § Low cake solids concentration (compared to centrifuge) § Low power § Sensitive to feedstock variations § Simpler O&M § Belt washwater usage § Limited cake odor § Odor potential (open equipment) production over time due to § High humidity vapors low-shear process § Space requirements

Table 6-15. Summary of Operational Issues for Belt Press Parameter Belt Filter Presses Flexibility § Simple adjustments respond to changes Ease of Operation § Most operators understand them Reliability § Mechanical equipment requires maintenance Environmental Footprint § Odor containment difficult

Expected Performance The expected performance of the BFPs is summarized in Table 6-16.

Table 6-16. Expected Performance of Belt Presses Item Units % Solids

Cake Solids percent solids by weight 16-20% Solids Capture percent solids by weight 90-98%

Centrifuges Centrifuges have been used in North America since the 1950s to dewater wastewater sludge. They fell out of favor during the 1970s but, with recent technical advances, they have regained a prominent place in this process use. The following paragraphs provide a description of centrifuge dewatering, the methods used to provide control, maintenance requirements, and several other special concerns.

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There are several types of centrifuges, one of which is solid-bowl decanter, a type used predominantly for wastewater sludge dewatering. There are four major pieces in a solid bowl centrifuge: bowl, scroll, main drive, and back drive.

Centrifuges have the capability to produce high solids content in dewatered biosolids. The description, performance and costs of centrifuges are presented in the following.

Description of Centrifuges. Decanter centrifuges operate by centrifugally accelerating sludge in a horizontal cylindrical bowl. This acceleration causes the denser solids to separate from the liquid and migrate against the bowl wall. Solids are then conveyed via auger to one end of the mechanism for discharge. The liquid filtrate overflows a weir and is discharged from the opposite end of the mechanism.

In this particular unit, feed sludge is introduced through a feed pipe in the hub of the bowl. The sludge is gradually accelerated before being fed into the cylindrical section of the bowl. Once fed into the bowl, solids separate from the liquid as a result of the centrifugal force being generated by the bowl and differences in specific gravity between the liquid and solids. The depth of this layer is regulated by adjustable weirs at the feed end of the machine. The centrate flows toward the weir, allowing finer particles additional time to settle.

The solids which have settled against the bowl wall are conveyed in the opposite direction by a scroll conveyor to the inclined section of the bowl. The bowl and scroll are controlled by separate drives and rotate at different speeds. The inclined section of the bowl allows for separation of the solids from the liquid pool and further dewatering of residual liquid. Solids are discharged from the bowl at the end of the inclined section.

Both liquid and solids discharge from the bottom of the machine via gravity. This controlled discharge and containment of the dewatering mechanism allows for localized odor control at the liquid and solids discharge ports.

This review of centrifuges looked primarily at the Westfalia decanter centrifuge. Additional centrifuges manufacturers include USFilter (Jspin), Sharples, Andritz (Guinard), Baker-Hughes (BIRD Machine), and Alfa-Laval (ALDEC). The layouts and price estimates developed for the Westfalia centrifuge would be similar to those of the other manufacturers.

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Table 6-17 presents a summary of advantages and disadvantages of decanter centrifuges.

Table 6-17. Summary of Advantages/Disadvantages for Centrifuges Advantages Disadvantages § High Solids. § High Maintenance cost, 2 to 4 year major maintenance required § Small Physical Footprint. (auger replacement), depending on operating scheme. § Automated operation. § High operating RPM, vibration and mechanical wear. § Closed operation enhances odor control. § High shear machine – may cause odor production with cake storage time.

The auger within the Westfalia Centrifuge has an operational life of 12,000-20,000 operating hours. This translates to 2 to 4 years between servicing of the wear plates, depending on operation scheme. Westfalia offers a service contract which delivers refurbished augers and does on-site replacement. The fee for this is $15,000 – $20,000, depending on the unit.

Additional regular maintenance reported by the manufacturer includes oil changes. The manufacturer did not provide service life information, however assumptions may be made that bearings, seals and other wear parts would require regular replacement given the high speed rotation and potential for vibration of the machine.

A general summary of operational issues with centrifuges is presented in Table 6-18.

Table 6-18. Summary of Operational Issues for Centrifuges Parameter Centrifuges Flexibility § Highly automated § Cake solids controlled by RPM and other parameters Ease of Operation § Low operator interface required § Sensitive to changes in feedstock Reliability § Daily operation § Higher frequency of maintenance required than other dewatering equipment Environmental Footprint Energy: § Somewhat more than belt press § High cake solids Materials: § High mechanical maintenance § Mechanical wear parts require semi-annual change-out. Chemicals: § Typically higher polymer use than belt press Emissions: § Better capture of gases from sludge compared with BFP

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Expected Performance. The expected performance of the centrifuge alternative is summarized in Table 6-19.

Table 6-19. Expected Performance of Centrifuges Centrifuge City-Based 2025 County Based- 2025 Item Units ADWF ADWF Cake Solids (low to medium Percent solids by weight 20 to 24% 20 to 24% solids machine) Solids Capture Percent solids by weight 95% 95%

Fournier Rotary Press The Fournier Rotary Press can produce relatively high solids in some dewatered biosolids. The press is described below.

Description. The Fournier rotary press technology operates by feeding flocculated sludge between two parallel, 4-foot diameter rotating, chrome-plated, stainless steel screens (400 micron) which rotate very slowly on a single shaft (typically between 1 to 3 rpm). Each disk set is called a channel. Each channel has a dry solids capacity ranging from 100 lbs/hr to 450 lbs/hr depending on feed solids concentration and dewaterability. Dewatering capacity is increased by adding channels. Filtrate passes through the screens as the sludge advances around the channel. The frictional force at the sludge/screen interface coupled with increased pressure caused by the outlet restriction produces the dewatered sludge cake. Each press can have from 1 to 6 channels installed on one gear box and center shaft.

The Fournier Rotary press has proven to be an effective dewatering device for blends of primary and secondary sludge as well as digested sludge. Developed in Canada, there are several plants running for over ten years with proven performance. The Fournier rotary press can typically achieve higher solids content than belt filter presses with only slightly higher polymer and power requirements. The low rotational speed has resulted in low maintenance requirements. The rotary press has enclosed dewatering channels minimizing odor control requirements. A summary of the advantages and disadvantages of the Fournier rotary press is presented in Table 6-20.

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Table 6-20. Summary of Advantages/Disadvantages for Fournier Rotary Press Advantages Disadvantages § Typically 3 to 5 percent higher cake solids than BFP, § One vendor for this particular technology. and 1 to 2 percent lower than centrifuge. Closer to § Only a few installations in the U.S.A. centrifuge than BFP. § Large compressed cake mass (12-inches tall by 12- to § Typically, polymer use slightly higher than BFP, but 16-inches long) is produced. Can require delumping. lower than centrifuge for same cake solids. § Moderate to relatively small foot print, larger than centrifuge, but smaller than BFP. § Automated operation. § Closed operation enhances odor control. § Low noise level. § Low rotational speed, vibration and mechanical wear. § Mixtures of primary sludge and secondary sludge dewater much better than straight secondary.

The rotary press typically outperforms a belt filter press by 3 percent to 5 percent in cake solids. The solids content performance of the rotary press is very dependent on throughput. The lower the throughput, the higher the cake solids. The higher the ratio of primary sludge, the higher the allowable throughput while still achieving high cake solids. Hampton NH has operated at throughput rates of 270 lb/hour achieving 27 percent cake solids with a sludge ratio of at least 40 percent primary and high grit levels. Dewatering trials in Portland ME indicated a good performance target was 240 lb/hour per channel with a target solids content of 24 percent for a sludge ratio of at least 50 percent primary and 240 lb/hour per channel with a target solids content of 21 percent for a sludge ratio of at least 40 percent primary.

One advantage of the Fournier press is its ability to self-compensate to some extent for changing feed conditions which results in low labor requirements for operation. The press compensates for feed and consistency changes by adjusting the feed rate based on inlet and outlet pressures. The polymer feed pump can be paced to the sludge feed pump to maintain the same polymer ratio. The units are also provided with PLC programming to periodically adjust the polymer feed ratio to optimize dewatering. The Fournier press is well suited to fully automated operation with minimal operator attention.

The very low speed and few moving parts on the rotary press lend it to being a very low wear and low maintenance piece of equipment. There are replaceable polyethylene wear parts and metal scraper knives that require periodic replacement depending upon the hours of operation. Typically, for machines running 24 hours a day, scraper replacement is about every 4 years. The Fournier press has had a good track record to date for low maintenance requirements. However, only smaller plants have used this technology. A general summary of operational issues is presented in Table 6-21.

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Table 6-21. Summary of Operational Issues for Fournier Rotary Press Parameter Fournier Rotary Press Flexibility § Improved. § Highly automated. § Percent Solids controlled by throughput. Ease of Operation § Reduced operator interface required compared to other technologies Reliability § Daily operation. § Low frequency of maintenance required. Environmental Footprint Energy: § Moderate HP required Materials: § Mechanical maintenance limited. Chemicals: § Small increase in polymer usage than BFP. Emissions: § Better capture of gases from sludge than BFP.

As a part of Laguna project, a sample was sent to Fournier as part of the dewatering equipment laboratory testing effort. The Fournier test results indicate very poor dewaterability with a predicted solids content of only 12 percent.

According to the Santa Rosa study, the rotary press does not appear to offer any performance improvement over the belt filter presses. The capital cost would be much more expensive than the belt filter presses or centrifuge alternatives. Consequently, the Fournier rotary press was not selected for more detailed analysis of capital and operating costs.

FKC Screw Press For some sludge types, the screw press can produce a dewatered cake intermediate in solids content between belt presses and centrifuges.

Description. The FKC screw press consists of a custom designed screw with a hollow shaft that steam can flow through to heat the sludge. The screw flights and hollow shaft increase in pitch and taper to reduce the available volume for the sludge to occupy, thus increasing the internal pressure and forcing water to drain out through the perforated cylinder that the screw turns inside of. The conditioned sludge is fed to an open feed box on top of the screw. Sludge dewaters first by gravity drainage out through the bottom while moving slowly down and into the screw flights. The speed of the screw is very slow and thus the units experience very little wear and very low maintenance. The power requirements are also low.

Screw presses have been used extensively in industrial applications especially in the pulp and paper industry. There are many manufacturers of screw presses with considerable differences in their dewatering capabilities. The FKC screw press design has proven relatively ineffective with digested municipal sludge, and they have not been used extensively due to higher capital cost and large size requirements. The advantages of the FKC screw press include high solids content, low rotational speed, low energy requirements and moderate polymer requirements. The press is enclosed

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minimizing odor control requirements. A unique feature of the FKC screw press is the ability to steam heat the dewatering screw and with pre-lime stabilization produce a class A sludge with very high cake solids as part of the dewatering operation. A summary of the advantages and disadvantages of the FKC screw press is presented in Table 6-22.

Table 6-22. Summary of Advantages/Disadvantages for FKC Screw Press Advantages Disadvantages § Typically, polymer use slightly higher than BFP, but § For digested sludge, difficult to dewater - lower than centrifuge for same cake solids. performance is questionable. § Automated operation. § One vendor for this particular technology. § Closed operation enhances odor control. § Only a few installations in the U.S.A. § Low noise level. § Very large footprint and space requirements. § Low rotational speed, vibration and mechanical wear. § Low power requirements § Works well on primary sludge

FKC screw presses have been installed to dewater municipal sludge at 20 municipal wastewater treatment facilities in Japan. In North America, they have 2 units installed at Victoriaville, Quebec (approximately 4 years old). Tallahassee, Florida is currently installing 2 units that were originally designed to dewater to Class B standards. The order was modified to convert the units to Class A, since Class B sludge is becoming less acceptable.

The screw press is most cost effective on primary sludge and in applications where continuous operation is desirable, since the unit can be smaller to dewater the same quantity over 24 hours than over 8 hours. Much of the interest in the FKC screw press is due to the capacity to meet Class A criteria using heat and pre-lime stabilization. Steam is used to heat the screw to provide supplemental heat thereby reducing the lime requirement to meet Class A criteria. EPA has indicated that the process is acceptable with documentation of the temperature-duration history. The capacity to stabilize and at the same time dewater to very high cake solids (30 percent to 35 percent or more) is attractive for facilities that desire to land spread Class A material. The negatives of this Class A process include very high polymer requirements due to the pre-liming, the need for a steam boiler, reduced throughput resulting in more and larger size units, and the need to operate 24-hours per day. It also requires a different screw design than one optimized for dewatering.

Due to its very limited use on digested sludges, and only at smaller plants, this technology is not sufficiently ready to consider for the SHDF.

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A general summary of operational issues is presented in Table 6-23.

Table 6-23. Summary of Operational Issues for FKC Screw Press Parameter FKC Screw Press Flexibility § Can be automated. § Percent Solids controlled by throughput and type of sludge. Ease of Operation § Low operator interface required Reliability § Daily operation. § Low frequency of maintenance reported. Environmental Footprint Energy: § Low power requirement. Materials: § Low mechanical maintenance reported. Chemicals: § Minor increase in polymer usage than BFPs. Emissions: § Better capture of gases from sludge than BFPs.

Dewatering/Drying Processes In addition to the dewatering options describe above, there are dewatering/drying combination processes available. Two of these units, the Centridry™ and J-Vap Dewatering/Drying System, are described below.

Centridry™ Centridry™ is a biosolids drying process developed by Humboldt-Decanter of Germany. The process combines centrifuge dewatering with flash air drying to produce a solids product with 50 to 60 percent solids. A five-month demonstration project was completed in 1998 at King County's South Plant in Renton, WA to evaluate the technology for possible implementation at the West Point Treatment Plant (West Point) and/or South Plant. The study evaluated the Centridry™ process and described the potential advantages and disadvantages of the process.

The following is a description of the major system components of the Centridry. The Centridry™ Centrifuge drying system is the combination of several dewatering steps in one continuous, enclosed process.

§ Clarification: Separation of solids from water takes place. § Compression: During transport of the solids by the screw conveyor, interstitial water is pressed out of the solids under the centrifugal force. The solids are further compacted by the Centripress™. § Drying: The dewatered sludge discharged is disintegrated into fine particles, which are entrained in the hot drying gas stream. § Hot Gas Generator: Drying gas is heated by a burner, which can be fired by a number of alternative fuels including fuel oil, natural gas, or digester gas.

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§ Product Separator: The dried particles are separated from the drying gas and discharged. § Condenser/Washer: Water vapor is removed from the drying gas in a condenser. § Gas Recirculation: A fan downstream of the cyclone feeds the major part of the drying gas recycle vapor to the Centridry™ Centrifuge. The remaining gas is blown to the condenser/washer by a second fan. A portion of the cleaned gas is recirculated to the hot gas generator and the excess is discharged through a further cleaning stage as exhaust gas.

The evaluation conducted at King County revealed that investment in the Centridry™ process could not be justified economically. Using unit costs for biosolids haul and application, and unit costs for operating cost components (labor, power, chemical, etc.), the added capital cost to implement Centridry™ could not be made up by reduced annual costs. However, the economic balance could change with changes in key unit cost components, especially the cost to haul and apply biosolids. It was recommended that King County continue to monitor the demand for biosolids, and especially the characteristics of biosolids that influence demand, and reconsider Centridry™, or other biosolids processes, when market conditions warrant.

The results of the initial Centridry™ Demonstration Project raised serious questions regarding Centridry™ product quality, especially with respect to dust from the product, as well as odors generated from the product after several days of stockpiling. Also, to achieve a Class A product from Centridry™, however, requires a large capital investment in not only Centridry™ but also a composting facility.

Based on the demonstration project conducted at King County, the Centridry™ process is not recommended for Clear Spring Ranch. This process was not included in the dewatering and drying options in the alternative analysis.

Vacuum/High Temperature Pressure Filters US Filter’s J-Vap Dewatering/Drying System dewaters and dries material (sludge, slurry, bulk solids, etc.) in one piece of equipment. The manufacturer claims that 95 percent dryness is possible.

The J-VAP Dewatering/Drying System includes a diaphragm plate filter press with vacuum/ evaporation technology. The J-VAP dewatering/drying system applications include: municipal water and wastewater sludges, industrial process slurries, and industrial wastewater and sludge.

The J-VAP system consists of a series of reduction chambers in which the dewatering and drying of the slurry takes place. The reduction chambers are clamped tightly together in the filter press module. The third component is the energy conversion module. This supplies heated water for the pressurization of the reduction chambers and also includes a vacuum system utilized during the drying stage of the cycle.

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During the first stage of the system's operation, slurry is pumped into the reduction chambers where the initial filtration takes place and the free liquid is removed. Since cake density is not a critical factor, short feed cycle times reduce the overall cycle time.

After the initial filtration cycle, the vacuum/drying cycle begins. The reduction chambers are pressurized with 150 to 180° F (65 to 80°C) hot water, and a vacuum is introduced. This causes the liquid remaining in the cake to evaporate. The drying time is set to achieve the desired solids reduction. After the drying cycle, the reduction chambers are separated and the dried cakes are discharged. The J-Vap system can achieve Class A material.

The technology has not been used on many larger plants and maintenance of the units has been troublesome and therefore is not recommended for Clear Spring Ranch. This process was not included in the dewatering and drying options in the alternative analysis.

Filtrate/Centrate Processing and Recycle The centrate generated during thickening and the filtrate or centrate produced from dewatering will need to be recycled for reprocessing. Thickening and dewatering processes will be considered for all alternatives evaluated. It is assumed that thickening to approximately 5.5 percent is achieved prior to digestion for all alternatives considered. Thickening and dewatering options for the SHDF have been described in detail above. The centrate generated from a thickening centrifuge will need to be treated before these return flows are transmitted back to the solids handling processes. After treatment, the centrate will be conveyed to the FSBs.

Processes considered for centrate treatment include a covered lagoon or an Upflow Anaerobic Sludge Blanket Reactor (UASBR). The Lower Fountain Water Reclamation Facility (LFWRF) is a proposed wastewater treatment facility currently being planned for the southern Colorado Springs Metropolitan Area to treat flows from the Jimmy Camp Creek Basin. Preliminary results of the ongoing Siting Study indicated that the Clear Spring Ranch area is the most favorable location for the LFWRF. Should this new WWTF be constructed at the Ranch, separate centrate treatment would not be necessary to treat the centrate produced from the thickening centrifuges, however the LFWRF would need to be designed to accept and treat the centrate flows.

The water generated from the thickening and dewatering processes will be directed to the FSBs and continue to the supernatant lagoons and on to crop or tree irritation. Other alternatives include piping to Las Vegas Street WWTP for treatment or treating and discharging at the SHDF.

Treated centrate or FSB supernatant piping and handling facilities are assumed to pump and spread this water for irrigation on about 300 acres of land at Clear Spring Ranch. There is approximately 1,500 acres due east and southeast of the SHDF (located on both the east and west side of Interstate 25) within the Clear Spring Ranch Property Boundary that possibly could be used for rangeland or crop irrigation.

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Dewatering Summary As discussed previously, initial screening of the four dewatering technologies revealed that the rotary press and screw press as well as the two dewatering/drying options were not well suited for application at the SHDF. As a result, a belt press or centrifuge dewatering will be considered in the alternatives analysis.

Dewatering of either digested or FSB harvested sludge assumes the following list of equipment:

§ Sludge feed holding tank § Centrifuge feed pumps § Solid bowl centrifuges (at least 4 units) § Polymer addition system § Cake pumps § Cake Storage § Centrate treatment system § Building

For the raw sludge dewatering the following list of equipment is estimated:

§ Pipeline from digester complex to power plant § Raw Sludge holding tank § Centrifuge feed pumps § Solid bowl centrifuges § Polymer addition system § Cake pumps § Cake storage tank § Centrate treatment system § Boiler feed pumps § Building

Dewatering will be included in many of the alternatives evaluated in Chapter 7. Either belt filter presses or centrifuge dewatering systems are recommended depending on the application.

Heat Drying

Heat drying systems involve the application of heat to evaporate water from sludge. This becomes a major advantage in reducing the weight of final product and in creating a biosolids product that is free of pathogens (Class A). This approach provides a product containing high solids content (generally above 80 to 90 percent dry solids content). In addition, if the process creates hard, dry, and similar-sized particles (usually between 1 and 5 mm in size) that are safe and easy to handle (non-dusty material), the product can be marketable as a fertilizer material. If the sludge is not stabilized through a digestion process prior to heat drying, the final product can be odorous,

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especially if it becomes re-wetted. Such re-wetting can occur during storage, but most often occurs at the final use site, if land applied.

In this study, heat or thermal drying of sludge is evaluated based on digested sludge (not raw sludge). Heat drying is more commonly accomplished with anaerobically digested (and dewatered) sludge feed material. Heat drying will be considered in the alternative analysis for the Class A material, beneficial use option. This option includes thickening prior to mesophilic digestion, centrifuge dewatering, and heat drying to produce a Class A marketable material.

Vendor-Provided Systems Heat or thermal drying systems are all essentially provided by vendors or manufacturers, and, therefore, each one is different due to its patented characteristics and the specific features and even the approach to drying taken by the vendor/manufacturer. Drying systems are often categorized according to whether they use a “direct’ or “indirect” drying approach as defined below.

Indirect Drying Technologies. In these systems, the heating source (steam or hot oil, typically) does not come into direct contact with the sludge. Instead, the heat is transferred to the sludge through paddles, mixers, or related devices. Therefore, the gas handling system is simpler for this approach, but there is somewhat different challenges in creating usable product and uniform particles with several of the processes available.

Direct Drying Technologies. These are systems whereby hot drying gas (normally heated air) is in direct contact with the sludge material. A large amount of particulates are picked up in these gas streams and major particulate/gas handling and treatment systems are required. Many of these systems recycle the exhaust stream to improve thermal efficiency and provide some thermal destruction of odorous compounds. However, there is more experience in direct drying (than indirect drying) systems for sludge, and more experience in creating fertilizer products.

Some of the more common heat drying systems are described briefly below. These systems are all designed to provide a well-graded product with relatively uniform particle sizes. This approach maximizes the value of the product.

§ ESP Dryer. The ESP process is a direct rotary drum process with once-through airflow. The dryer is a triple-pass, rotary dryer. A portion of the dried biosolids product exiting the dryer is recycled and blended with incoming dewatered biosolids to create the feedstock to the dryer. The gas/solids mixture entering the dryer is separated in cyclones and filters, and the dry product is classified by screens into oversize, market size, and fines. The oversize is crushed, mixed with fines, and recycled to mix with the incoming dewatered biosolids. The exhaust gases exiting the separation system are cooled and condensed in a wet scrubber, and the non- condensable fraction is heated in an afterburner to destroy odors. § Swiss-Combi. The Swiss-Combi process is a direct-drying, rotary drum process with air circulation. The dryer is a single-pass, rotary dryer. A portion of the dried

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biosolids product exiting the dryer is recycled and blended with incoming dewatered biosolids to create the feedstock to the dryer. The gas/solids mixture exiting the dryer is separated in a cyclone and fabric filter, and the dry product is classified by screens into oversize, market size, and fines. The oversize is crushed, mixed with fines, and recycled to mix with the incoming dewatered biosolids. The exhaust gases exiting the separation system are divided into two streams. The first stream is recycled to the dryer. The second stream is condensed, and the non-condensable fraction is heated in an afterburner to destroy odors. The afterburner also provides heat recovery from its flue gas. Some plants report drying raw sludge with this dryer. § Andritz. The Andritz process is a direct drying, rotary drum process with air recirculation. The evaporation process in the Andritz direct dryer takes place within a triple-pass, rotating drum. The high-speed air within the drum pulls the material through the drum until it is dry enough and, therefore, light enough to be lifted and pneumatically conveyed out of the drum. The Andritz dryer drum consists of three concentric arranged cylinders, so that the material to be dried flows through the innermost cylinder, back through the middle cylinder, and finally out through the outer cylinder. Flights on the inner walls of the cylinders lift the material and cascade it into the hot air stream. Andritz does not promote their system for raw primary sludge drying. § Seghers. The Seghers process is an indirect, tray dryer process. The vessel is vertically oriented, and hot oil is passed through the trays while the solids fall from one tray to the tray beneath, similar to a multiple hearth furnace. Dewatered biosolids mixed with recycled dry biosolids are fed through a top inlet in the vertical, multi-stage dryer. The dryer has a central shaft with attached rotating arms that are supported by axial-radial bearings at the bottom of the dryer casing. The rotating arms move biosolids from one heated tray to another in rotating, zigzag motion until it exits at the bottom as a dried, pelletized product. The rotating arms are equipped with adjustable scrapers that move and tumble the solids in thin layers over heated, stationary trays. Round pellets are formed through a pearling process. The solids feed preparation technique, in combination with the rolling across the heat trays, causes the pellets to grow from inside out, the way pearls are formed. § VA Tech. The VA Tech process is an indirect, fluidized bed process. Fluidization gases are distributed uniformly across the area of the dryer to keep the dry granules in an evenly floating motion. Inert gases are used for fluidization to provide a safe environment that requires minimal supervision. The heat exchanger is immersed in the fluidized layer to transfer all the energy necessary for evaporating the water from the wet sludge. Generally, steam or hot oil is used as the heat transfer media. The dryer hood collects the exhaust gases containing the evaporated water and some dust. These gases are recirculated for energy recovery and air treatment. The process produces a uniform granulated product that is 90 to 95 percent dry solids in a single stage. This process has recently been added to the Schwing line and is constructed in a vertical arrangement, which can reduce the process footprint, but can become quite tall.

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Most of the systems listed above are well suited for plants that are the size comparable to the SHDF. The final products are all pellets or granules of uniform size. Other dryer systems described below are more well suited to smaller plants and are reportedly less costly. The Fenton system had units sized to cover a range of production solids from 18 to 75 wet tons per day or 3.5 to 15 dry tons per day per dryer although Fenton normally has implemented dryers at plants of 5 mgd or less in capacity. The InnoDry system has units sized that are capable of handling a similar throughput up to 26 dry tons per day per dryer. The Komline Sanderson dryer comes in unit sizes that could handle a portion of or up to the full daily production at the SHDF. The product from these dryers is less uniform and has much larger variety of particle sizes. Consequently, the product has less “value” in the market place.

§ Fenton. The Fenton process is an indirect hollow plate dryer. Drying is done in a batch process to ensure compliance with EPA 503 regulations to produce a Class A product. The evaporator unit utilizes a patented sludge feeder with heated hollow discs using hot oil as an evaporating media. Programmed temperature control brings the dewatered cake to evaporation temperatures quickly then controls the temperature at optimum levels to produce a desired dryness. Exhaust air is scrubbed to remove particulates and minimize emissions. Standard size units can be provided for average daily production of 18 to 75 wet tons per day. Fenton also offers a product purchase option for terms of one to three years to provide product disposition. § INNOPLANA. The INNOPLANA drying (InnoDry) process utilizes a two-step drying system that incorporates both indirect and direct drying. The first stage employs a thin film evaporator utilizing hot oil as an evaporating media. Dried solids leave the first stage at approximately 45 to 50 percent dry solids through an extrusion/chopping mechanism. This chopper shapes the product into spaghetti shaped strands of a selected size and length. The chopped material passes onto a belt dryer which passes the product through a hot air stream utilizing waste heat recovered from the first stage to produce a final dried product up to 90%+ dry solids. Process safety is enhanced because the drying process and dried product are largely dust free and temperatures in the plant are below ignition limits. This largely dust free operation provides vapor condensate and exhaust air with low emissions. Through use of an integral heat recovery system this second stage requires little additional energy to produce the desired dryness. This has been reported to represent approximately 30 to 40 percent energy savings over other drying systems. This process has been in operation for approximately four years in Europe. The plant in Merenschwand Germany has been in operation since 1996 and is available for pilot trials. § Komline-Sanderson. The Komline Sanderson process is an indirect hollow paddle dryer using hot oil or steam as the heat transfer media. The dual counter-rotating shafts with intermeshing wedge-shaped paddles promote thorough mixing and convey the product through the drying process. No internal adjustments are needed

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on any of their moving parts. It’s high torque mixing system enables it to take the dewatered cake through the plastic range without the need to recycle some of the dry product. The variable speed system conveyor system allows the unit to handle a wide range of solids loads and concentrations. These units are also equipped with an explosion relief system for added safety.

Process Operations Considerations Heat dried product characteristics and heat dryer air emission controls are described below.

Dried Product Characteristics. The dried product is generally valued on its nitrogen content for use as a fertilizer amendment providing that it meets the required physical characteristics such as particle size, hardness, and density. To achieve the optimum or desired product, dryer systems may need ancillary equipment items such as screens, grinders, and even a pelletizer/compactor. Dryer systems also employ recycle of dried product to the feedstock at a variable rate to be determined for the specific feedstock and desired product characteristics. In some instances, additives may be mixed with the sludge material to achieve certain desired characteristics. These additives may include oils to assist in binding of product, nutrients to change fertilizer components, and chemical suppressants to minimize heating and potential combustion of product.

Anaerobically digested sludge, when heat dried, usually provides a good, usable product. Removal of hair and plastic debris is important for good product quality, and, therefore, sludge screening is a good approach when a high-quality marketable product is desired.

When raw sludge is heat dried, the product is typically more odorous than dried digested sludge because little stabilization of the organic material has occurred. The low moisture content in the product is the primary defense against biological activity. If any significant moisture accumulates in the product, then active biological activity is initiated and odor can become significant. For instance, when dried raw sludge is spread on a field, rainfall prior to soil incorporation of the material would likely create an odorous situation.

Heat Dryer Air Emissions Controls. All exhaust air stream organics from sludge heat dryers would need to be controlled to limit the concentrations of air contaminants. Some control is achieved within the initial heating process. For instance, temperature and excess oxygen control enables balancing nitrogen oxides (NOx) against carbon monoxide (CO). Whereas, the former increases at increasing temperatures, and the latter decreases at decreasing temperature. This is similar to what happens with automobile emissions. Typically a venturi scrubber installed just downstream of the sludge dryer will remove such mater-solid pollutants such as particulate matter and sulfur oxides to below regulatory limits. Engineered biological oxidizers, chemical oxidizers, or recycling of this air stream back to an existing process for reuse would then be designed to remove the remaining air pollutants to acceptable levels. Dryer systems have normally been able to meet necessary air emission regulations in the United States.

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The air emission that attracts the highest public awareness is invariably odor. Although the process air can be well oxidized and controlled through the use of the aforementioned systems, the ventilation air from buildings, storage tanks and truck loading is a much larger air flow and requires treatment before discharge. Essentially, all of the proposed systems require similar size buildings with consequently similar exhaust airflows to be treated. Bulk media biofiltration and/or activated carbon systems are often installed to insure adequate odor control at all times.

Development of Drying Option Various thermal drying systems could be used at the SHDF. Heat drying would provide a reliable means of producing a Class A product that could be disposed of more readily.

Fuel Source (Digester Gas) The 2001/2002 SHDF digester gas production is described in Table 6-24. The average gas volume production for 2001 and 2002 is 705,000 and 666,000 cubic feet per day, respectively. After boiler gas usage, the remaining gas sent to the flare waste burner was 315,000 and 365,000 cubic feet per day, respectively. The 2001 and 2002 minimum to maximum day flare gas ranges from 115,000 to 592,000 cubic feet/day and 91,000 to 582,000 cubic feet/day.

Table 6-24. SHDF Digester Gas Production (Cubic Feet per Day) 2001 Average Max day Min day Total 705,000 908,000 480,000 Flare 315,000 592,000 115,000 Boiler 390,000 683,000 177,000 2002 Total 666,000 850,000 366,000 Flare 365,000 582,000 91,000 Boiler 301,000 586,000 85,000

On peak winter days, there is barely enough gas production to heat the digesters. This is because of the relatively thin sludge feedstock (approximately 3 percent solids feed).

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Air Drying of Biosolids Air drying can achieve Class A pathogen reduction requirements, but actual pathogen reduction needs to be demonstrated for each site.

Air Drying and Associated Processes Air drying allows biosolids to dry naturally in the open air. Slurries are usually applied to a depth of approximately 9 inches onto paved beds. The sludge is left to drain and dry by evaporation. Sand beds have an underlying drainage system. Mechanical mixing or turning is frequently added to paved or unpaved basins. The effectiveness of this process depends on the local climate. Drying will occur faster in warm, dry weather and therefore, it is assumed only feasible in the warmer seasons at the SHDF – perhaps 7 or even 8 months of the year.

Since air drying of digested, dewatered biosolids has not always produced Class A material, additional treatment will be necessary to provide greater assurance. Such Class A treatment can be provided by higher-temperature digestion (thermophilic), increased storage time in FSBs, or perhaps some combination of these processes. If the Class A technology used does not comply with EPA’s time/temperature requirements, sampling of the final product in batches to prove that it meets EPA’s Class A pathogen density limits would be required. The Class A material would then be hauled off-site for beneficial use through agricultural land application, land reclamation, or various other end uses.

Air-Drying Operations in Colorado Several facilities in Colorado have adopted air-drying as a cost-effective and efficient disposal method, with the benefit of a resulting Class A biosolids product. The climate in Colorado is generally well suited for air-drying, especially in the summer months, which increases the feasibility and reduces the expense of conducting an air-drying operation. The benefits and considerations involved in operating an air-drying facility are illustrated through the experiences of three facilities, described below.

Beginning operations in 1993, the Louisville Wastewater Treatment Plant operates one of the longest-running air-drying facilities in Colorado. Three acres of asphalt pads produce approximately 500 dry metric tons of product annually. The overall cost after centrifuge dewatering is about $100/dry ton, which includes all materials and daily maintenance. The Class A product is sold for $10/cubic yard to non-residents, and is free for residents. Other than the city itself, which uses a significant portion of the product for city projects, consumers consist mostly of homeowners. Over time, they have made improvements to their process and have created a sustainable and successful operation. Improvements have included: decreased frequency of mixing and use of a biofilter to extract air to decrease odor; aligning and shaping air-drying piles according to the prevailing winds and increasing the height of a perimeter berm to reduce dust problems; and fully utilizing an existing lagoon system to effectively manage runoff.

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The Pinery Water and Wastewater District’s drying and composting operation has been in place since 1995. They produce 180-200 dry tons per year. The current cost per ton, following belt-press dewatering, is $100-$118/dry ton to create a Class A composted product. Currently, the product is sold at $12.50/ton. They have a good customer base for selling compost product including some golf courses as well as a considerable amount of residential customers. Though the air-drying operation is a successful and beneficial method of biosolids management, the future of the operation is questionable given odor complaints due to prevailing winds and atmospheric inversions along the creek bed in early spring. However, having built a consumer base for the product, they are able to explore other options that will involve selling a product, though other processes will invariably incur greater costs.

The Mesa County Solid Waste Management program enjoyed brief success with a composting operation before operations were halted as a result of complaints of perceived odor. Due to the perceived odor problem, and fear of potential further complaints, a fully constructed biosolids air- drying facility built on a recompacted clay pad is currently not in operation. Even though air-drying biosolids may be a beneficial and cost-effective method for Mesa County, they are unable to proceed without support from the Board of Commissioners.

Larger-Scale Air Drying Facilities There are several larger-scale biosolids air drying facilities that use a process train similar to the potential system described here for the SHDF.

At Chicago (Metropolitan Water Reclamation District of Greater Chicago) perhaps the largest biosolids air drying facility in the world has operated for at least 40 years. After digestion and about 2.5 years of lagoon storage/treatment time, air drying is conducted in warmer seasons to achieve about 60 to 65 percent solids material for large-scale beneficial use in Illinois. The highly stable lagooned material does not create high odor levels from the paved drying areas, although the District receives occasional odor complaints due to the location in the middle of suburban Chicago.

At San Jose, California, anaerobic digestion of sludge is followed by about 3 years of lagoon storage/treatment (200 acres of lagoons). In warmer, non-rainy months, air drying of the lagoon slurry (about 5 percent solids) is air dried to 75 percent solids. About 25,000 tons of final product are created each year and the product is tested to confirm it meets Class A standards. Final product is used as landfill cover material at a nearby landfill. As at Chicago, the biosolids coming from long- term lagoon storage/treatment are quite stable, such that air drying operations do not create odor problems. New hundred-million-dollar commercial developments have occurred within 1+ mile downwind of the San Jose lagoon/drying site without problems.

At Eugene, Oregon, anaerobic digestion is followed by lagooning (2+ years average in facultative lagoons), then belt press dewatering and warm-season air drying on paved beds. This facility has diversified over the years so that some product is composted, some belt press cake is land applied, and some air-dried product is also provided for beneficial uses. Biosolids production is from the 30 mgd Eugene/Springfield WWTP.

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Approach for SHDF Air Drying Based on lessons learned from the above and other facilities, considerations and concepts for an air- drying operation include the following:

§ Large-scale biosolids air drying can be successfully conducted if the biosolids have been digested/stabilized through long-term lagooning prior to air drying. Even with this level of treatment, some buffer distance is still required between drying beds and public use areas. § Stormwater runoff must be contained and controlled on-site. § Demonstration-scale testing of air drying should be conducted before constructing a large project to confirm evaporation rates, equipment needs, odor issues, and operational requirements. § With actual dried product quantities from demonstration-scale testing, Colorado Springs Utilities can determine user and private contractor interest in the specific product that would be produced at the SHDF. Product marketing work can also be conducted if it appears there is potential for sale of Class A material.

Information below compares air drying of slurry material (from dredging FSBs at 4 percent solids), to air drying of cake material. The analysis is conducted on the year 2025 biosolids quantities from the County-based projections, so this compares a large-scale drying system.

Air-Drying Slurry The following shows assumptions and analysis of the slurry drying approach based on 13,000 dry tons/year of product at 4 percent solids – 230 acre-ft/year of water.

§ 18 inches of net evaporation/year estimated from slurry/cake drying in warmer months § 150 acres of paved slurry drying beds, with levees, etc. § Costs for paved beds include levees, leveling, sludge feed piping, stormwater control, roads, and related work at $2.25/sq ft = $15 million. § An additional 15 acres is needed for product stockpiling, roads, etc. at cost estimate of $1.50/sq ft = $1 million. § Equipment includes 3 mixing/turners (Brown Bear, etc), 2 front loaders, with cost estimate of $1 million. § Total construction cost estimate is: $17 million § Annualized capital cost based on 20-year life would be $65/dry ton.

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§ Annual O&M costs assume 8 month/year operation with staff of 3, plus fuel, maintenance, etc. estimated to be $300,000 per year, or $23 per dry ton. § Total capital and O&M cost estimate of about $88/dry ton.

Air-Drying Dewatered Cake The following is an analysis of the dewatered cake drying approach based on 13,000 dry tons/year of cake at 18 percent solids – 43 acre-ft/year of water.

§ 12 inches of net evaporation/year estimated from cake drying in warmer months. § 43 acres of paved cake drying beds § Costs for paved beds include some leveling, stormwater control, roads and related work at estimated cost of $1.75/sq ft = $3.3 million § Equipment includes 2 dump trucks, 2 mixing/turners (Brown Bear, etc.), 2 front loaders with cost estimate of $1 million. § Total construction cost is: $4.3 million § Annualized capital cost based on 20-year life would be $16/ dry ton. § Annual O&M costs assume 8 month/year operation with staff of 3, plus fuel, maintenance, etc. estimated to be $300,000 per year, or $23/dry ton. § Total capital and O&M cost estimate of about $39/dry ton.

Typically, dewatering costs are higher than air drying the dredged slurry material directly to avoid mechanical dewatering. However, the area required (165 acres), is very difficult to achieve and probably not possible at the site. Also, this large an area of drying (150 acres) exposes Colorado Springs Utilities to more odor potential. The more feasible option is to assume air drying with the dewatered cake option.

Recirculating Fluidized Bed Boiler (RFBB)

Colorado Springs Utilities is considering a major project at the Nixon Power Plant to install a RFBB. The rationale for the project is to take advantage of new boiler technology for power generation that allows the use of coal without having extensive scrubbers to prevent acid rain. As a sideline to the boiler project, and as part of this Masterplan, Colorado Springs Utilities is considering the possibility of disposing of raw sludge in the boiler. There is a negative energy value to disposing of the sludge in this way, but there are significant avoided costs in not needing to digest and dispose of the biosolids. The effort in the Masterplan for this alternative is limited to consideration of raw sludge dewatering and treatment of the centrate or belt press supernatant produced.

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For the purposes of this Masterplan, it has been assumed that a new pipeline would be extended from the existing pipeline to the power plant, and that no additional pumps would be required to transport the sludge. A dewatering facility would be built at the site of the RFBB, which would dewater the slurry to 20 percent solids, and the cake would be conveyed directly into the RFBB, using progressive cavity pumps. The centrate from the dewatering operation would be treated to reduce the BOD before being introduced to the existing FSBs for further treatment. At least for the initial few years, the digesters would remain partially functional, to provide a backup sludge treatment method, and to provide an active microbial environment in the FSBs to help treat the centrate. We would anticipate that the feed to the RFBB would gradually increase, with the possibility that some digestion would continue for several years, if not indefinitely. Digestion, FSB and DLD operations would be greatly reduced.

Off-Site Beneficial Use and Disposal Modes As identified earlier in this Chapter, mesophilic digestion alone will not produce a Class A material. However there are several biological and thermal processes that can be added to a mesophilic digestion process train to achieve a Class A material, as previously described, or digestion can be changed to thermophilic operation.

Beneficial use alternatives will be considered that will produce Class A material. Modified digestion with added dewatering and air-drying as well as dewatering and heat drying will be evaluated. These options assume off-site transport of Class A product for land application or as a fertilizer amendment product. Chapter 5 describes in detail beneficial use options and marketing of these products considered for Colorado Springs Utilities.

Other methods of disposal were investigated and are described below. Options include emergency back-up disposal with Parker Ag Services, LLC (Parker Ag) and local landfill options. These emergency back-up options are not recommended alternatives, however planning level cost estimates are listed for information purposes. Information on prior Colorado Springs Utilities compositing studies is also included.

Land Application of Class A Material Parker Ag was contacted regarding preliminary costs and information for transport and application of Class A product. Parker Ag estimates approximately $20/dry ton for them to haul and land apply air dried or heat dried product (50 percent solids or greater). This is less expensive than Class B material because the Class A product can be sold to offset some of the costs.

Associated marketing costs would be an initial investment and be reduced significantly over time. For Parker Ag (or Colorado Springs Utilities) to market the product to homeowners or other fertilizer facilities it is estimated at approximately $3/dry ton in the first year of operation. The second year would be approximately a break-even point, and in the third year Colorado Springs Utilities could see a cost reduction. Initially the product would be given at no cost or minimal cost to try to build a market or clientele. After the market and client base is established, presumably by

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the second and third years, Colorado Springs Utilities could gradually see a cost reduction by the third year.

Class A and B biosolids have been used successfully in Colorado for mine site reclamation. The best known of these sites is the Climax Mine near Leadville. The biosolids are mixed with local soils to provide a topsoil mixture capable of sustaining a plant cover to stabilize mine tailings.

Emergency Back-Up DLD Disposal Options Parker Ag Services (PAS). PAS could accept biosolids from the SHDF for disposal on a planned or emergency basis. PAS has found that the market demand exists for biosolids, and may be able to effectively find reuse modes for biosolids in the event that the SHDF is unable to dispose of biosolids in the DLD. The cost for contract, off-site, hauling and use will vary based on tonnage, time of year and other factors. Locally in the Colorado Springs area, PAS could find uses for approximately 10 percent of biosolids generated by the SHDF using land application (Class B material). For more than 10 percent of the SHDF biosolids, PAS would have to haul the biosolids outside the Colorado Springs area. PAS has mobile belt presses to remove moisture from the sludge, which would decrease weight and consequent hauling costs.

In order for PAS to accept the biosolids, they would need to meet heavy metals criteria and have at least Class B material (Class A would be preferred since there is a greater demand for surface application than for injection).

Costs for off-site land application of FSB-harvested biosolids (current loading) on an emergency basis would be $215/dry ton, at 5 percent total solids. In 2025, it is estimated costs will increase to $250-300/dry ton.

Landfill Disposal. There are several landfills in the Colorado Springs area that will accept biosolids. Table 6-25 presents a summary of the local landfills, approximate haul distances, and tipping fees. The landfills require the sludge to be proven nonhazardous and to have no free water as determined by the EPA paint filter test.

Sanitary landfill disposal is an emergency back-up option and may be used for short periods when the primary use/disposal options are not available. This alternative assumes transporting biosolids that has been stabilized and dewatered to a landfill.

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Table 6-25. Landfill Summary Approx. Distance Approx. Tipping fee, from Clear Spring Haul cost, Disposal Site $/cu. yd. Ranch, miles $/cu. yd. Comments US Waste Fountain $10 10 $17.50 Assumes 10 cu. yd container. Landfill—Sludge Cake Costs are $150 for haul plus $25 for a container liner. US Waste Fountain $10 10 $7.50 Assumes 20 cu. yd container. Landfill—Dried Sludge Costs are $150 for haul (no liner required). Colorado Springs $10 20 $5.00 Estimate based on $90 per load Landfill—Sludge Cake and 18 cu. yds. Per load.

Midway Landfill—Sludge $8 10 $5.00 Estimate based on $90 per load Cake and 18 cu. yds. Per load.

Composting Colorado Springs Utilities has previously researched and evaluated biosolids composting at the facility and determined it not feasible at this time. Beginning in May 1997, a Biosolids Composting Pilot Project was completed by The Scotts Company. The purpose of the study was to evaluate different composting techniques and determine the most feasible technique for Clear Spring Ranch. A 5 to 10 acre parcel was designated as the “pilot project area”, with an active composting area of 2 acres. Ten test windrows were in place. During the project, an operational plan was generated, metals data, microbial parameters, and dry weight was recorded. In October 1998, this project was determined not feasible and not expanded to full scale.

In April 1999, Colorado Springs Utilities investigated composing options again. Options included off site land application, on-site land application, and on-site composting. In January 2000, Colorado Springs Utilities determined that these options were not favorable, but would continue to re-evaluate the potential to compost in the future. The basis for not selecting composting is based on costs and impact on wastewater rates, lack of data from previous studies needed for decision making, the need for future evaluation of other alternatives, and regulatory concerns. Due to the amount of previous research on composting, it was not included in the alternative analysis.

Initial Disposal/Beneficial Use Process Screening The biosolids disposal and beneficial use evaluation was conducted in two steps. First, an initial list of sludge disposal and beneficial use options was generated for consideration. Second, the initial list of options was reduced to a final list which received a more detailed evaluation.

Several alternatives for disposal and beneficial use are available for Colorado Springs Utilities to consider. These alternatives are presented in Table 6-26 and are categorized into four options: disposal, beneficial use (Class B); beneficial use (Class A), and other beneficial use. Retained alternatives were selected by the project team through discussions in workshops and review of

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Technical Memoranda. Brief statements are included in Table 6-26 to indicate the potential of these disposal and beneficial use methods and practices for Colorado Springs Utilities.

Table 6-26. Initial Assessment of Sludge Disposal and Beneficial Use Options Assessment For Colorado Further Evaluation Warranted? Disposal/Beneficial Use Method Springs Utilities (Retain or Reject) Disposal Options Improved Existing System Existing System/Primary Method Retain of Disposal. Lined DLD Soil is natural “liner” which Reject minimizes groundwater impacts. Additional groundwater removal techniques will be investigated under Improve Existing System Alternative. Sanitary Landfill disposal Common method in United Retain as emergency backup States, if properly dewatered. Incineration/ash disposal in dedicated There are serious concerns about Reject incinerator regulatory constraints, public perception, and environmental impacts. Bulk solids disposal in sludge Monofill Difficulty in locating and Reject permitting sludge-or biosolids only monofills. Other DLD Disposal (i.e. Parker Ag) Could accept biosolids for Retain as emergency backup disposal on a planned or emergency basis. Beneficial Use Options – Class B On-site land application – digested slurry If stabilized and good quality Retain (Evaluate under Improved product, can be considered. Existing System) Off-site land application – digested slurry or Land Application should be Class Reject cake A Material only. Off-site land application – air dried Potential use in RFBB. Retain (Evaluate under RFBB) Alkaline products – land application Little need for alkaline material on Reject nearby soils. Off-site landfill cover or land or mine Common use across United Reject reclamation States, if sufficiently dewatered/dried. See Class A Option for evaluation. Beneficial Use Options – Class A Heat dried product – marketing/distribution Increasing development of this Retain approach, and technologies to heat-dry sludge. Composted product – marketing/distribution 2 previous studies completed, Reject determined not feasible.

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Assessment For Colorado Further Evaluation Warranted? Disposal/Beneficial Use Method Springs Utilities (Retain or Reject) Alkaline material marketing/distribution High temperature, odor potential Reject is significant. Local product use is questionable. Vitrification/bio-bricks/similar products Very limited experience and high Reject cost. Make cement product Very limited experience and high Reject cost. Gasification/char products Limited experience and odor Reject concerns. High costs. Land application, landfill cover, or land If high quality product, can be Retain reclamation – cake product considered. Common use across United States Land application, landfill cover, or land If high quality product, can be Retain reclamation – air-dried product considered. Common use across United States Other Beneficial Use Raw/digested sludge into recirculating Colorado Springs Utilities is Retain fluidized bed boiler (RFBB) currently considering RFBB installation.

Alternative Selection Table 6-27 presents five alternatives selected for evaluation, which are derived from Table 6-26 above. The selected five alternatives are evaluated in Chapter 7.

Table 6-27. Selected Disposal/Beneficial Use Alternatives for Evaluation Final Material Concentration, Alternative Option (% solids) Disposal Options 1 Modified or Improved FSB/DLD System 16-26% Beneficial Use – Class A 2 Class A (Heat Dry) and Beneficial Use 90% 3 Class A (Digestion) and Beneficial Use (dewater and air-dry FSB-harvested biosolids) 40-80% 4 Class A (Digestion) and Beneficial Use (dewater and air-dry 50 percent of digested 16-80% sludge) Other Beneficial Use 5 Sludge Cake to Recirculating Fluidized Bed Boiler (RFBB) 16-26%

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Chapter 7. Alternative Evaluation

Overview The most feasible or promising alternatives have been developed in sufficient detail for development of capital and O&M costs. This chapter summarizes and compares these alternatives, and includes recommendations. The following five alternatives have been selected for evaluation and are described below.

§ Alternative 1 – Modified or Improved FSB/DLD System § Alternative 2 – Class A (Heat Dry) and Beneficial Use § Alternative 3 – Class A (Digestion) and Beneficial Use (Dewater and Air-Dry FSB- Harvested Biosolids) § Alternative 4 – Class A (Digestion) and Beneficial Use (Dewater and Air-Dry Portion of Digested Slurry) § Alternative 5 – Sludge Cake to Recirculating Fluidized Bed Boiler

It should be noted that estimated costs in this Chapter have been refined in Chapter 11 for the recommended alternative only.

Alternative 1 – Modified or Improved FSB/DLD System Alternative 1 assumes modifications to the existing system operation. The addition of thickening, modified/improved FSB/DLD systems, and dewatering is assumed. A schematic displaying the components of Alternative 1 is shown on Figure 7-1.

Thickening Prior to Digestion This alternative includes addition of thickening prior to digestion. Providing a thicker feed to the digestion process is desirable for several reasons:

§ Prevent excessive detention time in the Sludge Main. § Reduce the number of digesters that need to be operated in the near-term. § Cut sludge heating requirements as a result of reduced digester feedrates. § Delay the time that additional digesters would need to be constructed.

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Figure 7-1. Alternative 1 – Modified or Improved FSB/DLD System

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There are several potential types of thickening processes that could be used – such as gravity belt thickeners, centrifuges, dissolved air flotation thickeners, drum thickeners, etc. However, with the characteristics of the solids arriving at the SHDF (fermented, low pH, and extremely odorous) the thickening process would need to be fully contained. Therefore, centrifuges are recommended for this application. A thickening system at the SHDF would need to encompass the following elements:

§ Thickened sludge storage/mix tank to handle a few hours (maximum) of sludge flow and provide a consistent feed to the thickening centrifuges - size and details need further evaluation. § Three or four thickening centrifuges, with feed pumps, polymer system, power supply, control systems, etc., all located in a new structure near the current Sludge Main discharge point and adjacent to the digesters. § Thickened sludge pumping facilities to feed 6+ percent solids to all digesters (normally estimated to be 5.5 percent solids, but capability should exist to pump at least 6 to 6.5 percent solids). Centrate treatment system – assume Upflow Anaerobic Sludge Blanket Reactor at this time. § Treated centrate or FSB supernatant piping and handling facilities is assumed to pump and spread this water for irrigation on about 300 acres of land at Clear Spring Ranch. There are approximately 1,500 acres due east and southeast of the SHDF (located on both the east and west side of Interstate 25) within the Clear Spring Ranch Property Boundary that possibly could be used for rangeland or crop irrigation.

Digestion Conversion of the four pre-existing (pre-1998) digester covers to submerged-fixed type and from an unconfined gas lance system to a mechanical draft tube mixing system is recommended sometime in the future, depending on equipment condition, to prevent the floating covers from causing problems as they age. The primary reasons to install submerged-fixed covers are:

§ Achieve additional capacity in each digester. § Foam control. § Better mixing and automated mixing control. § Reliability.

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Additional FSBs In order to remain under the design FSB loading rate of 20 lbs. VS / 1,000 ft2 / day, two additional FSBs are recommended to accommodate the 2025 Colorado Springs projected loadings (10 FBSs in service, 1 FSB being dredged). Seven additional FSBs are recommended to provide adequate capacity based on 2025 El Paso County projected loading (15 FSBs in service, 1 FSB being dredged).

It is recommended Colorado Springs Utilities develop procedures for keeping track of the amount of solids within each FSB. This is important for various operational reasons including: (1) need to know if basin is full – overfilling the basin creates odors, and difficulty in floating the dredge; (2) need to plan for future dredging operations, to insure that too many basins don’t reach “full” status during the same year; (3) need to monitor the thickness of sludge within basins to confirm basin health and inventory status; and (4) determine if dredging activity has removed the planned quantity of solids.

It is also assumed that the dredge will need to be rehabilitated during the planning period. For the County projections, a new dredge and rehabilitation of the existing dredge is assumed.

Improved and Modified DLD System For the City-based projections, it is assumed that tillage (frequency to be determined by testing) will increase evaporation and the application rate of 7 inches/year. Therefore no additional DLD is assumed. It is assumed that one TerraGator should be added during the planning period. Field testing is recommended to confirm future operational needs.

For the County-based projections, it is assumed that frequent disking of dewatered cake would improve the evaporation. An additional 100 acres of DLD is assumed. A 36-acre expansion is expected in 2004; therefore, an additional 64 acres will be necessary. Since the TerraGators will no longer be injecting liquid sludge into the DLD for the County projections, new spreading equipment (3 units) is assumed.

Dewatering Dewatering is assumed for Alternative 1 (County-based) option. This alternative assumes belt filter press dewatering of FSB-harvested material prior to DLD application.

As discussed previously, initial screening of dewatering technologies in Chapter 6 revealed that belt presses or centrifuges could be used depending on the alternative.

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Alternative 2 - Class A (Heat Dry) and Beneficial Use Alternative 2 includes addition of heat drying of digested and dewatered sludge to produce a Class A product. The addition of thickening, reduced FSB/DLD systems, dewatering, and a heat drying system is assumed for Alternative 2. A schematic displaying the components of Alternative 2 is shown on Figure 7-2.

Thickening Prior to Digestion Four thickening centrifuges, a thickened sludge storage/mix tank, thickened sludge pumps, centrate treatment system, and treated centrate piping and handling for Clear Spring Ranch irrigation are assumed for this alternative.

Digestion Conversion of the four existing digester covers to submerged-fixed type and from an unconfined gas lance system to a mechanical draft tube mixing system is recommended sometime in the future, depending on equipment condition, to prevent the floating covers from causing problems as they age.

Reduced FSB Operation This alternative assumes reduced FSB units in service since digested sludge will be dewatered and heat dried. The FSBs will continue to handle a reduced quantity of digested sludge when the primary operation is not in service for any reason. However, it is assumed that the FSB dredge will need to be rehabilitated during the planning period for both City-based and County-based projections.

Reduced DLD Operation This alternative assumes reduced DLD acreage since the sludge will be heat dried to a Class A product and hauled off site to be used as a fertilizer amendment. The DLD will continue to be used as a backup or reduced operation when the primary operation is not in service for any reason.

Since the TerraGators will no longer be injecting liquid sludge into the DLD, new spreading equipment for back up use (2 units for City-based and 3 units for County-based projections) is assumed.

Dewatering This alternative assumes centrifuge dewatering of digested material prior to heat drying.

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Figure 7-2. Alternative 2 – Class A (Heat Dry) and Beneficial Use

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Heat Drying System Heat drying systems involve the application of heat to evaporate water from sludge. This becomes a major advantage in reducing the weight of final product and in creating a biosolids product that is free of pathogens (Class A). This approach provides a product containing high solids content (generally above 80 to 90 percent dry solids content). In addition, if the process creates hard, dry, and similar-sized particles (usually between 1 and 5 mm in size) that are safe and easy to handle (non-dusty material), the product can be marketable as a fertilizer material. Various thermal drying systems could be used at the SHDF.

Heat drying will involve a capital investment to establish the necessary physical plant and, because of this, a market study should be done by Colorado Springs Utilities beforehand. If such a study identifies a potential market for dried and pelletized sludge, this option could be pursued. Establishing and operating a drying and pelletizing operation could be done by Colorado Springs Utilities or by a private firm. This would be part of a technical and economic feasibility study that would complement a market study.

Alternative 3 - Class A (Digestion) and Beneficial Use (Dewater and Air-Dry FSB-Harvested Biosolids) Alternatives 3 and 4 are similar, with the only difference being if the digested sludge continues to the FSBs for further digestion prior to dewatering or is dewatered immediately following digestion (for a portion of the flow). Alternative 3 assumes dewatering of FSB-harvested biosolids. Alternative 4 assumes dewatering a portion of the digested sludge.

Alternative 3 includes the addition of air drying to produce a Class A product. The addition of thickening, modified digestion, additional FSBs, a reduced DLD system, belt press dewatering, and an air drying operation is assumed. A schematic displaying the components of Alternative 3 is shown on Figure 7-3.

Thickening Prior to Digestion Four thickening centrifuges, a thickened sludge storage/mix tank, thickened sludge pumps, centrate treatment system, and treated centrate piping and handling for Clear Spring Ranch irrigation are assumed for this alternative.

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Figure 7-3. Alternative 3 – Class A (Digestion) and Beneficial Use

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Digestion Modifications to the mesophilic digesters are assumed for Alternative 3. This digestion modification is a relatively simple approach to Class A digestion – i.e., raising the temperature to thermophilic operation on the four newer digesters, and repiping to make the four older digesters a second-stage digestion system. Heating requirements for thermophilic digestion are higher than for mesophilic digestion, but the thickening system greatly reduces the quantity of sludge that must be heated to thermophilic temperatures.

Conversion of the four existing digester covers to submerged-fixed type and from an unconfined gas lance system to a mechanical draft tube mixing system is recommended sometime in the future, depending on equipment condition, to prevent the floating covers from causing problems as they age.

Additional FSBs In order to remain under the design FSB loading rate of 20 lbs. VS / 1,000 ft2 / day, two additional FSBs are recommended to accommodate the 2025 Colorado Springs projected loadings (10 FBSs in service, 1 FSB being dredged). Seven additional FSBs are recommended to provide adequate capacity based on 2025 El Paso County projected loading (15 FSBs in service, 1 FSB being dredged).

It is recommended Colorado Springs Utilities develop procedures for keeping track to some extent of the amount of solids within each FSB as described above in Alternative 2.

The existing dredge will need to be rehabilitated during the planning period. For the County projections, a new dredge and rehabilitation of the existing dredge is assumed.

Reduced DLD Operation This alternative assumes reduced DLD operation. Modified digestion with air drying (in warm seasons) should produce a dried Class A product that would be hauled off site for beneficial use, land application, etc. The DLD will continue to be used as a backup system and on a reduced operation schedule during winter months, when air-drying is not feasible due to weather.

Since the TerraGators will no longer be injecting liquid sludge into the DLD, new spreading equipment for back up use and during winter months (2 units for City-based and 3 units for County- based projections) is assumed.

Dewatering This alternative assumes belt filter press dewatering of FSB-harvested material prior to air drying.

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Air Drying Operation Class A air dried product can be produced at the SHDF assuming thermophilic digestion is used as described above. Following storage and further digestion in the FSBs, dewatering with belt filter presses would be used since this type of dewatering provides the least odor from subsequent cake air drying.

Alternative 4 - Class A (Digestion) and Beneficial Use (Dewater and Air-Dry Portion of Digested Slurry) Alternative 4 assumes dewatering a portion of the digested slurry.

Based on the 2025 Colorado Springs projection, it is estimated that approximately 20 percent of the flow would need to be removed and dewatered in order to avoid constructing additional FSBs and DLD areas in the future. For the 2025 El Paso County projection, it is estimated that approximately 50 percent of the flow would need to be removed and dewatered in order to avoid constructing additional FSBs and DLD areas in the future.

Alternative 4 includes addition of air drying to produce a Class A product. The addition of thickening, modified digestion, belt press dewatering, and an air drying operation (for a portion of the flow) is assumed. A schematic displaying the components of Alternative 4 is shown on Figure 7-4.

Thickening Prior to Digestion Four thickening centrifuges, a thickened sludge storage/mix tank, thickened sludge pumps, a centrate treatment system, and treated centrate piping and handling for Clear Spring Ranch irrigation are assumed for this alternative.

Digestion Modifications to the mesophilic digesters are assumed for Alternative 4. The digestion modifications are a relatively simple approach to Class A digestion – i.e., raising the temperature to thermophilic operation on the four newer digesters and repiping to make the four older digesters a second-stage digestion system.

Conversion of the four existing digester covers to submerged-fixed type and from an unconfined gas lance system to a mechanical draft tube mixing system is recommended sometime in the future, depending on equipment condition, to prevent the floating covers from causing problems as they age.

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Figure 7-4. Alternative 4 – Class A (Digestion) and Beneficial Use (Portion)

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FSBs Since a portion of the loading will flow to dewatering immediately following digestion, the FSBs will be offloaded somewhat. It is assumed that approximately 20 percent (City-based) to 50 percent (County-based) of digested sludge will be air dried to minimize the footprint and air drying odors.

It is recommended Colorado Springs Utilities develop procedures for keeping track to some extent of the amount of solids within each FSB as described in Alternative 2.

In addition, the existing dredge will need to be rehabilitated during the planning period.

DLD Operation This alternative assumes reduced DLD operation. Modified digestion with air drying (in warm seasons) should produce a dried Class A product that would be hauled off site for beneficial use, land application, etc. The DLD will continue to be used for 20 percent (City-based) to 50 percent (County-based) of the load and during winter months, when air-drying is not feasible due to weather.

Since the TerraGators will no longer be injecting liquid sludge into the DLD, new spreading equipment for back up use and during winter months (2 units for City-based and 3 units for County- based projections) is assumed.

Dewatering This alternative assumes belt filter press dewatering of approximately 20 percent (City-based) to 50 percent (County-based) of digested material prior to air drying. The remaining portion will continue to the existing FSB/DLD operation.

Air Drying Operation Class A air dried product can be produced at the SHDF assuming thermophilic digestion is used as described above. Following digestion, approximately 20-50 percent of the sludge will be conveyed to belt filter press dewatering (this type of dewatering provides the least odor from subsequent cake air drying).

Alternative 5 – Sludge Cake to Recirculating Fluidized Bed Boiler Alternative 5 assumes transporting raw sludge directly to the power plant for RFBB fuel. For the purposes of this Masterplan, it has been assumed that a new pipeline would be extended from the existing pipeline to the power plant, and that no additional pumps would be required to transport the sludge. A dewatering facility would be built at the site of the RFBB, which would dewater the slurry to 20 percent solids, and the cake would be conveyed directly into the RFBB, using progressive cavity pumps. The centrate from the dewatering operation would be treated to reduce the BOD before being introduced to the existing FSBs for further treatment. At least for the initial

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few years, the digesters would remain partially functional, to provide a backup sludge treatment method, and to provide an active microbial environment in the FSBs to help treat the centrate. We would anticipate that the feed to the RFBB would gradually increase, with the possibility that some digestion would continue for several years, if not indefinitely. Digestion, FSB and DLD operations would be greatly reduced. A schematic displaying the components of Alternative 5 is shown on Figure 7-5.

It should be noted that if a thickening system were in place, all or part of the centrifuges could be converted from thickening to dewatering with minor modifications. The dewatered cake could then be transported to the RFBB by hauling or pumping.

Dewatering In general, the system would be designed to be implemented in two phases; the first to be built now, sized to provide service through the year 2015, and another phase to be operational in 2015 that would handle capacity through 2025. For the purposes of this estimate, centrifuge dewatering was assumed rather than belt presses, because operationally they are more compatible with the Utility’s automation philosophy, and they are slightly more expensive (about 10 percent) to buy, so the estimate is conservative.

For the purpose of providing a planning level estimate of the sizing and cost of the equipment for this alternative, the system was assumed to consist of the following:

§ A pipeline from the digester complex to the boiler site. For the purposes of this estimate, twin 10-inch pipelines 10,000 feet long were assumed, giving sufficient capacity through 2025. § Raw sludge holding tank. A small surge tank is included to provide a small buffer between operations, and to give the feed pumps proper suction. A second tank would be added in Phase 2. § Dewatering feed pumps. Two centrifugal pumps, capable of 250 gpm, with a third added in Phase 2. § Solid bowl centrifuges. Install three at 220 gpm each, adding a fourth in Phase 2. § Polymer system. Initial installation will handle through 2025. § Dewatered cake pumps. To transport cake from centrifuge cake hopper to cake storage tank. One per centrifuge. § Cake storage tank. To provide buffer between operations. Sized for 12 hours detention at today’s flow rates. Assumed to be a steel tank lined with coal tar epoxy. Add second tank in Phase 2.

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Figure 7-5. Alternative 5 – Sludge Cake to RFBB

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§ Centrate treatment system. Due to the plug-flow digestion in the pipeline, the centrate will be very high in volatile fatty acids and other organic material. To avoid odor problems in the FSBs, treatment is required. The use of a packaged Upflow Anaerobic Sludge Blanket Reactor was assumed, with one skid-mounted installed in Phase 1 and another in Phase 2. § Boiler feed pumps. Same as dewatered cake pumps. § Building. A concrete block building with steel roof and gross dimensions, 100 feet x 80 feet with a 24-foot eve height was assumed. The building will be sized to house both phases.

RFBB The Utility is doing a detailed analysis of the RFBB for the purpose of power generation. Any estimate of capital or operating cost for the RFBB is not in the scope of this Masterplan.

Reduced Digestion This alternative assumes reduced number of mesophilic digester units in service, with a gradual phasing out of digester operations. There may be some amount of digester activity indefinitely, as described above.

Reduced FSB Operation This alternative assumes reduced number of FSB units in service, with the main purpose of the FSBs being for final treatment of the centrate.

Reduced DLD Operation The operation of the DLDs will be greatly reduced, depending on the level of digestion.

Economic and Noneconomic Comparison of Alternatives Economic information for the above-described alternatives is summarized in Table 7-1. Pertinent information about the cost information in Table 7-1 is provided here and a list of cost and economic criteria are included in Appendix A:

§ All sludge and biosolids processing systems from thickening through final use/disposal are included for each complete alternative. § Grit and screenings processing and disposal are not included in the analysis since there is adequate capacity in the existing DLD for these. § No inflation in either capital cost or O&M cost is included in this analysis. § All costs and prices are defined for year 2003.

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Table 7-1. Solids Alternative Cost and Economic Comparison Estimated Costs based on City of Colorado Springs Projections Estimated Costs based on El Paso County Projections Alternative 3 - Class A Alternative 4 - Class A Alternative 4 - Class A Alternative 1 – (Digestion) and (Digestion) and (Digestion) and Modified or Alternative 2 - Beneficial Use Beneficial Use Alternative 3 - Class A Beneficial Use Alternative 5 – Improved Class A (Heat (Dewater and Air-dry (Dewater and Air-dry Alternative 5 – Sludge Alternative 2 - Class (Digestion) and Beneficial (Dewater and Air-dry Sludge Cake to FSB/DLD Dry) and FSB-Harvested 20-50 percent of Cake to Recirculating Alternative 1 – Modified or A (Heat Dry) and Use (Dewater and Air-dry 20-50 percent of Recirculating Cost Category System Beneficial Use Biosolids) Digested Slurry) Fluidized Bed Boiler Improved FSB/DLD System Beneficial Use FSB-Harvested Biosolids) Digested Slurry) Fluidized Bed Boiler Capital Costs (dollars): Sludge Thickening 1 $16,500,000 $16,500,000 $16,500,000 $16,500,000 $16,500,000 $16,500,000 $16,500,000 $16,500,000 Digestion Modifications 2 $2,100,000 $2,100,000 $2,100,000 $2,100,000 Digester Covers/Mixing 3 $6,000,000 $6,000,000 $6,000,000 $6,000,000 $6,000,000 $6,000,000 $6,000,000 $6,000,000 FSB Expansion 4 $4,000,000 $4,000,000 $14,000,000 $14,000,000 FSB Dredge and Rehab 5 $100,000 $100,000 $100,000 $100,000 $400,000 $100,000 $400,000 $100,000 DLD Expansion 6 $250,000 DLD Equipment 7 $300,000 $500,000 $500,000 $500,000 $750,000 $750,000 $750,000 $750,000 Dewatering 8 $15,000,000 $15,000,000 $12,000,000 $18,000,000 $15,000,000 $15,000,000 $15,000,000 $12,000,000 $18,000,000 Heat drying $26,000,000 $37,000,000 Air drying $3,000,000 $1,500,000 $4,300,000 $2,200,000 RFBB 9 9 9 Total Construction Costs (includes 30 $26,900,000 $67,100,000 $50,200,000 $41,700,000 $18,000,000 $52,900,000 $79,350,000 $63,050,000 $43,650,000 $18,000,000 percent contingency) Engineering, legal, admin, etc. @ 25% $6,725,000 $16,775,000 $12,550,000 $10,425,000 $4,500,000 $13,225,000 $19,837,500 $15,762,500 $10,912,500 $4,500,000 Total Capital Costs $33,625,000 $83,875,000 $62,750,000 $52,125,000 $22,500,000 9 $66,125,000 $99,187,500 $78,812,500 $54,562,500 $22,500,000 9 O&M Costs (dollars/yr): Sludge Screening at BSPS $50,000 $50,000 $50,000 $60,000 $60,000 $60,000 Pumping Sludge Main $330,000 $330,000 $330,000 $330,000 $330,000 $400,000 $400,000 $400,000 $400,000 $400,000 Sludge Thickening $570,000 $570,000 $570,000 $570,000 $750,000 $750,000 $750,000 $750,000 Digestion - Mesophilic $500,000 $500,000 $670,000 $670,000 Digestion - Thermo/Meso $550,000 $550,000 $730,000 $730,000 Digestion - Minimal $250,000 $330,000 FSBs $130,000 $90,000 $130,000 $130,000 $35,000 $190,000 $125,000 $190,000 $190,000 $35,000 Supernatant Irrigation 10 Dredging $120,000 $80,000 $120,000 $120,000 $35,000 $180,000 $120,000 $180,000 $180,000 $35,000 DLD $240,000 $80,000 $80,000 $200,000 $50,000 $240,000 $80,000 $80,000 $200,000 $50,000 Dewatering $1,100,000 $850,000 $220,000 $2,400,000 $1,300,000 $1,600,000 $1,300,000 $800,000 $3,500,000 Heat Drying $1,450,000 $2,150,000 Air Drying Operation $250,000 $135,000 $330,000 $180,000 Final Product Disposition 11 N/A $0 11 $190,000 $50,000 11 N/A $0 11 $285,000 $180,000 11 Total Annual O&M $1,890,000 $4,250,000 $3,120,000 $2,355,000 $3,100,000 $3,730,000 $5,955,000 $4,305,000 $3,670,000 $4,350,000

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1 Sludge Thickening includes the following components: · Thickened sludge storage/mix - 150,000 gallon tank. · Four thickening centrifuges, with feed pumps, polymer system, power supply, control systems, etc. · New structure near the current Sludge Main discharge point and adjacent to the digesters. · Thickened sludge pumping facilities to feed 6+ percent solids to all digesters. · Centrate treatment system – assume Upflow Anaerobic Sludge Blanket Reactor at this time. · Treated centrate or FSB supernatant piping and handling facilities is assumed to pump and spread this water for irrigation on about 300 acres of land at CSR. 2 Cost estimated to convert 4 newer digesters to thermophilic digestion and to convert 4 older digesters to thermo/mesophilic digestion. 3 Cost based on escalated values from the 1998 expansion project. 4 Construction costs for additional FSBs include impermeable lining are estimated to be $400,000 per acre or $2 million per FSB. 5 Assumes $100,000 for rehab and/or $300,000 for new Dredge. 6 For Alternative 1 (City based projections), tillage is recommended to promote evaporation, which should eliminate or limit DLD expansion. For Alternative 1 (County based projections), dewatering is assumed to reduce the amount of future DLD required- 100 acres are assumed at $2500/acre. 7 TerraGator is assumed to cost $300,000 (Alternative 1 - City). Two spreaders are assumed for Alternatives 2-4 (City) at $250,000/spreader. Three spreaders are assumed for Alternatives 1-4 (County) at $250,000/spreader. 8 Assumes Belt Filter Press or Centrifuge dewatering (see detail on each alternative). 9 The Utility is doing a detailed analysis of the RFBB for the purpose of power generation. Any estimate of capital or operating cost for the RFBB is not in the scope of this Masterplan. RFBB feed is assumed to be pumped through a pipe to the RFBB (pumping and piping included in dewatering estimate). 10 Supernatant irrigation costs will be determined. It will be the same for all alternatives. 11 For Alternative 2, revenue derived from dried pellet sales is assumed to cover the costs of marketing and distribution for Class A dried pellets. Alternative 5, to be determined with more detail on RFBB operation.

Note: Estimated costs have been refined in Chapter 11 for the recommended alternative.

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Table 7-2 provides non-economic ratings of the solids alternatives and overall comparison scores. Weighted ratings are indicated in the table. An explanation of the ratings is contained in Appendix B. A majority of these ratings are subjective in nature, and, therefore, the final scores are subject to interpretation. Accordingly, the total scores should be considered in a broad context.

Table 7-2. Non-Economic Comparison Alternative 3 - Alternative 4 - Class A Class A (Digestion) (Digestion) and Beneficial and Beneficial Alternative 5 Alternative 1 – Alternative 2 - Use (Dewater Use (Dewater – Sludge Modified or Class A (Heat and Air-dry and Air-dry Cake to Improved Dry) and FSB- 20-50 percent Recirculating Score FSB/DLD Beneficial Harvested of Digested Fluidized Bed Rating Factor Weighting System Use Biosolids) Slurry) Boiler Technical Flexibility 3 3 4 4 3 1 Ease of O&M 5 5 2 2 1 4 Proven System 3 5 4 5 3 1 Reliability 5 5 3 3 3 2 Ability to Construct 3 4 1 3 4 4 Environmental Odor Potential 5 5 3 3 2 3 Product Use 2 1 5 4 3 1 Water Impact 4 3 4 3 3 4 Air Impact 3 3 1 3 3 1 Community/Local Acceptability 3 4 3 2 2 3 Regulatory/Permits 5 4 2 3 3 2 End Use Control 5 5 3 2 2 5 Trucking 2 5 2 1 2 5 Community/Beyond Local Acceptability 3 2 5 4 3 3 Regulatory/Permits 3 4 2 3 3 2 Trucking 2 5 2 1 2 5 Total Scores 229 159 161 144 163 Note: The higher the score, the more desirable the alternative.

Table 7-2 above shows a summary of the non-economic evaluation factors used for this analysis. The “Score Weighting” column applies relative importance to each of the items in the table. Each of the factors are evaluated using a relative score between 1 and 5, with 5 being the most favorable. The scores are multiplied by the weighting factor, and the values are summed to give a numerical score at the bottom.

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For this analysis, continuation of the existing system as shown in Alternative 1, with improvements as needed for capacity, regulations, and equipment replacement is preferred.

Overall Comparisons and Conclusions A Net Present Value (NPV) analysis was done on the estimated capital and operating costs, using a time period of 20 years and an interest rate of 5 percent. It was assumed that some of the capital was spent in year one (2005), and the remaining capital in year 11 (2015), dependent upon estimated project timing. O&M costs begin in year one. These assumptions have some error, because capital expense will probably be spread out into two or more projects, as capacity needs develop, and O&M is likely to start after construction is complete. A more detailed analysis will be possible during the preliminary design phase, but in this plan, it is assumed that the same errors apply to each of the alternatives and the comparisons are valid. Table 7-3 shows the NPV comparison, for both the City-based and the County-based projections.

Table 7-3. Alternative Net Present Value Comparison Alternative City-based Projection County-based Projection 1 $61,800,000 $123,400,000 2 $154,000,000 $200,200,000 3 $111,600,000 $144,200,000 4 $89,200,000 $116,400,000 5 $77,500,000 $101,200,000

As can be seen from the table, continuing the system as it is and making improvements as needed for added capacity, to prevent struvite buildup in the digesters, and to replace worn out equipment is the least expensive alternative (Alternative 1) in the near term.

The NPV analysis shown here indicates that Alternative 5 has the lowest cost for the County-based projections, and next-lowest cost for the City-based projections. It should be noted, however, that all costs are not yet included in this analysis for Alternative 5. For example, the cost burden of evaporating the water contained in the sludge will lower the value of the electricity produced in the boiler (or increase the amount of fuel needed). Also, additional permitting work, and perhaps additional air monitoring equipment, will be needed when the sludge feed is introduced to the RFBB.

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Chapter 8. Use of Digester Gas for Energy Production

Overview The purpose of this investigation is to identify possible beneficial uses for the energy contained in the digester biogas, and to make recommendations for future biogas utilization.

Biogas Utilization Colorado Springs Utilities currently uses the biogas from their digesters to provide fuel for boilers to generate hot water to heat the buildings in the winter, to provide the heat required to heat the incoming biosolids slurry to the digester operating temperature, and to maintain the digesters at temperature.

Colorado Springs Utilities has done a significant amount of work investigating gas utilization, including testing of microturbines, obtaining vendor quotes for drying equipment, and studies as part of the predesign documents for the previous expansions. Recent increases in the cost of energy and the expectation of future increases may make cogeneration or other gas utilization a more attractive option. This study takes a new look at the economics of cogeneration, as well as considering several other potential uses of the biogas.

This chapter presents a discussion of available technologies for digester gas utilization, and a screening for feasible alternatives. The potential alternatives include:

§ Cogeneration of electrical power using either microturbines of conventional engine generators. § Engine-driven mechanical equipment. § Utilization of gas in the nearby power plant. § Adsorption chillers. § Direct conversion of biogas to either electrical energy (fuel cell) or a salable product.

Potential alternatives were screened initially based on "ballpark" estimates for capital and operating costs, plus qualitative assessments for process risk and reliability. Based on this assessment, three alternatives were chosen for further evaluation, planning level cost estimates were performed, and a twenty-year life-cycle cost estimate comparison was performed.

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Available Digester Gas

Table 8-1 summarizes the gas available for utilization in the year 2002.

Table 8-1. Digester Gas Production and Usage (scf) Month Waste Gas Boiler Gas Total January 7,309,174 15,014,984 22,324,158 February 5,581,246 13,666,500 19,247,746 March 6,984,799 13,278,682 20,263,481 April 10,053,184 10,825,296 20,878,480 May 12,460,257 8,245,203 20,705,460 June 15,005,276 5,286,403 20,291,679 July 15,487,110 4,612,656 20,099,766 August 15,317,635 5,400,763 20,718,398 September 12,966,502 5,539,054 18,505,556 October 11,929,743 8,048,637 19,978,380 November 9,073,537 10,651,383 19,724,920 December 6,687,241 14,527,034 21,214,275 Average 10,737,975 9,591,383 20,329,358

As can be seen from the data in Table 8-1, there is a significant variation in how much gas is wasted and how much is needed for heating the facility and process, but there is little variation in the amount of gas produced each month. The year 2002 will be used as a basis in the economic comparisons, with escalation in future years. The existing waste gas flares, with a capacity of 80,000 scfh are adequate through the planning period.

Cogeneration

General Cogeneration systems simultaneously convert fuel into two useful forms, electric or mechanical power and thermal energy. A cogeneration system achieves a much higher overall energy efficiency than a conventional utility power plant by capturing and using waste heat to satisfy thermal requirements for other processes. Cogeneration facilities harness as much as 75 percent of the energy content of the fuel source, compared to typical utility power plant efficiencies of 28 to 35 percent. The improvement in fuel to useful energy efficiency represented by cogeneration reduces total fuel consumption with direct environmental and air quality benefits. For cogeneration to be practical, the application site must have a potential use for both thermal energy and for either electrical or mechanical power.

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Dual Fuel System The existing system for using the boilers for building and process heat is designed with a backup of using diesel fuel to fire the boilers. This alternate fuel is very expensive to operate, and is considered to be only useful as an emergency backup.

Internal Combustion Engine Most wastewater treatment plant cogeneration systems use an internal combustion engine to drive an electric generator or other essential mechanical equipment such as large pumps or blowers. The net fuel to power efficiency for this first step ranges from 20 to 30 percent. A heat recovery system captures waste heat from the engine exhaust and cooling water, usually recovering up to 50 percent of the available heat energy. The system can be designed to optimize either power or heat production depending on the primary energy demand specific to the site. Generally, recovered heat in excess of the plant's thermal needs will be wasted.

Low pressure, clean-burn engines are typically available in sizes up to 1,000 kW. Depending on the engine manufacturer and application, these engines require fuel pressures in the range of 1 to 3 psig. A gas pressure booster blower can be used to increase the fuel pressure to the engine.

Engines can be designed to run on digester gas, a blend of digester and natural gas, or natural gas alone. In spite of the gas cleaning system in place at Clear Spring Ranch, the engine fuel system must be designed to accommodate contaminants in the digester gas stream including condensate, particulate, and H2S.

Maintenance Properly designed internal combustion engine-generators can operate reliably on digester gas with reasonable maintenance costs. Total maintenance costs including engine overhauls and heat recovery equipment are typically approximately $0.015 per KWH. This maintenance cost is based on actual costs from similar projects, and on engine maintenance service agreements at other treatment plants.

Cogeneration Alternative For the purpose of evaluating potential energy savings from digester gas fueled cogeneration systems, the following design parameters were used:

§ An engine heat exchanger inlet water temperature of 160 degrees F. § An engine heat exchanger outlet water temperature of 200 degrees F. § A site elevation of 5,520 feet. § A digester gas fuel energy value of 600 Btu/scf, LHV. § A maximum digester gas input pressure of 2 psig. § An average electrical power unit cost of $0.025/kWh.

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The 2002 annual average digester gas production was 688,000 scf/day, or 17.2 million Btu/hr. Although currently used only for plant heating needs, this energy could be utilized to generate both electrical power and heat through a cogeneration system.

The planning level estimates for evaluation of the cogeneration alternative compared to the other gas utilization alternatives were done using the estimated cost for purchasing a new generator.

Estimated values of the evaluation factors for cogeneration are:

Alternative Capital Cost, Maintenance Cost, Operability & Description $ / KW $ / KWH* Technical Risk** Reliability*** Cogeneration $1,590 $0.015 Low Medium * Repairs and preventative maintenance. Energy cost is considered to have no cost for biogas. ** It is a commonly used technology. *** Compared to electrically driven pumps and blowers with 95 percent plus reliability.

Alternative Generation Technologies In addition to the standard synchronous generator set, several other types of generation equipment have been considered. These include:

§ Induction generators, which utilize all the gas produced and don't require paralleling equipment to connect to the power company. § Microturbines, which are more efficient than reciprocating engines and are reputed to be reliable due to having several small units rather than one large one. The experience with microturbine testing at Clear Spring Ranch has resulted in additional conservatism in estimated O & M costs in this report. § Fuel Cells, where the biogas is used in a fuel cell to directly generate electricity.

Induction Generators In the past, induction generators have been used for a number of small operations, such as animal feeding operations, because the equipment is simple, and there were fewer barriers set up by the power companies to connect to the power grid. More recently, the power companies have imposed the same type of restriction and safeguards on induction generators as for synchronous generators. In addition, the paralleling equipment needed for synchronous generators has been modernized and made less costly.

Based on our conversations with equipment suppliers, the alternative for induction generators is considered to be equal with synchronous generators, and, because of the existing equipment at the facility, implementation of an induction generator would be more expensive.

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Microturbines Microturbines would have the following evaluation factors:

Alternative Capital Cost, Maintenance Cost, Operability & Description $ / KW $ / KWH Technical Risk Reliability Microturbines $2,800* $0.010 High Medium * Cost for new system

Because microturbines are still an emerging technology, and due to some operating issues with the test units at the Clear Spring Ranch, care must be taken when comparing them with other technologies. The equipment appears to have great potential in the future, when certain problems are worked out.

Microturbines have the following potential advantages and disadvantages.

Advantages: § Higher efficiency than reciprocating engines. § Modular design allows multiple units, so machines can be started and stopped to match gas production. § Lower scheduled maintenance cost. § Multiple units improves reliability. § High operating temperatures improve heat recovery efficiency.

Disadvantages: § Experience at Clear Spring Ranch has shown higher maintenance cost than anticipated by manufacturers. § Compressor required for fuel gas feed. § Fuel gas must be clean and free of entrained water and siloxane. § Untried technology. § Major maintenance must be done by factory personnel.

Fuel Cells A fuel cell is a device that produces electricity directly by combining hydrogen and oxygen in the presence of anodes. It is possible to use biogas as a fuel for a fuel cell, but processing of the biogas to make it suitable fuel is required. For digester gas, moisture and sulfur containing contaminates must be reduced to low concentrations, and then conversion of the fuel to hydrogen (reforming) is required. Due to high thermal efficiency, the potential to operate pollutant-free, and the extreme

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simplicity of the fuel cell, this technology is very appealing. There are currently several fuel cell operations operating on digester gas. Units are operating at:

§ Yonkers, NY. § Deer Island, MS. § Portland, OR. § Calabasas, CA. § Cologne, Germany.

While the existing projects are a technical success, they are reputed to be not viable economically. Fuel Cell technology for biogas utilization offers the following advantages and disadvantages.

Advantages: § Direct generation of electricity with no moving parts. § High thermal efficiency. § Pollution-free operation. § Expected low operation and maintenance costs. § Fuel cells produce electricity based on feed, so they can match generation with fuel supply.

Disadvantages: § High capital cost due to emerging technology. § Biogas must be completely cleaned up, with removal of sulfur compounds, water and other material. Cleanup will result in pollution side streams. § Cleaned gas must be converted to a form suitable for use in a fuel cell. Process is called "reformation." § New technology is costly, and the "bugs" are not worked out.

Evaluation factors associated with fuel cell energy usage are as follows:

Alternative Capital Cost, Maintenance Cost, Operability & Description $ / KW $ / KWH Technical Risk Reliability Fuel Cells $7,500* $0.02 High Medium * includes extensive gas clean-up equipment

While fuel cells may be the only method considered for cogeneration at some time in the future, the technology is not ready at this time. This technology will not be included in further considerations.

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Other Uses for Gas

Operation of Process Equipment Most of the electrical power used at wastewater treatment facilities drives large mechanical equipment such as pumps, compressors, and blowers. Much of this equipment runs continuously except for periodic shutdowns for scheduled maintenance work. With appropriately sized engines mechanically connected to a blower or pump and a waste heat recovery system, the plant could achieve the high energy efficiency of cogeneration with a relatively simple mechanical system. This approach avoids the complex and expensive electrical switchgear and safety devices required for a direct link between on-site generators and the plant power grid.

Because there are no large motors operating at the Clear Spring Ranch Facility that would make this a practical alternative, it will be dropped from further consideration.

Air Conditioning Absorption chillers can provide cooling for refrigeration or air conditioning. There are two types of absorption chillers, direct-fired and indirect-fired. Indirect-fired chillers utilize hot water or steam as a primary energy source. Indirect-fired chillers are sometimes used with a hot water boiler or cogeneration system to make use of heat that would otherwise be wasted during the summer.

Indirect-Fired Absorption Chiller. Single-effect lithium bromide type absorption chillers can produce 45 degree F chilled water using hot water at 190 degrees F as their primary energy source. Carrier is a typical supplier of this type of absorption chiller. Carrier’s smallest absorption chiller has a capacity of 80 tons of cooling when used with 190 degree F heating water and 80 degree F cooling water. This chiller requires approximately 20,000 Btu per ton of cooling or about 1.6 million Btu/hr of 190 degree F hot water.

A chiller this size could air-condition a building of about 32,000 square feet. Smaller indirect fired absorption chillers are not available and absorption chillers do not operate well at greatly reduced loads or with significant changes in their applied cooling loads. Absorption chillers also require a significant amount of cooling water. An 80-ton absorber would need about 320 to 400 gpm of well- strained cooling water. The cost of an 80-ton absorber is about $40,000 to $50,000.

The Energy Recovery Building is the largest continuously occupied area at the plant that requires cooling during the summer. The chiller for this building is a 70 ton unit. This is below the minimum size appropriate for an indirect-fired absorption chiller.

Due to the minimum capacity of an absorption chiller, and the need for cooling water that is not available, an indirect-fired absorption chiller would not be a feasible alternative for use with a boiler or cogeneration system.

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Direct-Fired Absorption Chiller. Direct-fired absorption chillers typically use natural gas as the primary fuel source, but some suppliers manufacture chillers to operate on propane. Only a few suppliers manufacture small direct-fired absorption chillers. The Robur Corporation manufactures the Servel chiller, a direct-fired absorption chiller that can operate on natural gas or propane fuel. The Servel chiller is available in sizes from 5 to 25 tons. The 25-ton chiller has a cooling capacity to cool an area of about 10,000 square feet. This chiller size would be sufficient to provide cooling for the Digester Complex.

The Servel chillers use R-717 as refrigerant, otherwise known as ammonia. The footprint of a 25-ton Servel direct-fired chiller is 21 feet long by 4 feet wide. The unit operating weight is approximately 4,800 pounds. The 25-ton unit is air cooled, and requires 3.75 kW of electric power during operation. A Robur indirect-fired chiller of this size requires a natural gas input of 482,500 Btu/hr (higher heating value).

The Robur Corporation has indicated that they have not used digester gas as a fuel source with their Servel direct-fired chillers. This manufacturer also recommended that if digester gas was to be used with one of their chillers, a smaller 5-ton unit should first be purchased and field-tested to determine if digester gas would work properly with their equipment. Pre-treatment of the digester gas would also be required to remove hydrogen sulfide and moisture.

A 25-ton Servel direct-fired chiller costs about $40,000. Digester gas pre-treatment equipment, electrical equipment, and mechanical piping would cost about $150,000 in addition to the chiller cost. The potential energy savings of this alternative are outweighed by considering the limited number of suppliers who manufacture chillers of this size, high initial costs, and the risk of a chiller system not functioning as intended with digester gas fuel. Therefore, a direct-fired chiller is not a feasible alternative for digester gas use.

Evaluation factors associated with direct fired chillers are as follows:

Alternative Capital Cost, Maintenance Cost, Operability & Description $ / KW $ / KWH Technical Risk Reliability Direct Fired Chiller $1,500 $0.2 Medium Medium

Conversion of Biogas to Methanol There is an emerging technology for conversion of biogas to methanol and then possibly adding fats and oils to the methanol to produce an additive for diesel fuel that would make diesel cleaner burning and make the fuel a better lubricant. The technology involves cleaning the gas to remove moisture, H2S, and other contaminants, and then using a thermocatalytic process to convert methane to methanol. This process may be in tomorrow's headlines, but as of today, there is no track record of success.

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Energy Source for Nearby Industries In many municipalities, the facility is located in an area where there are nearby industries that can use the biogas. The viability of such an application depends on how the industry's energy need matches the gas production, how clean it needs to be, and BTU content requirements. If this were a viable option, the economics would be excellent, even if gas cleanup were required.

While there are no available industrial gas users in the vicinity, the possibility of using the gas to generate electricity at the nearby Nixon Power plant should be considered. This scenario would include piping low pressure steam from the power plant to the digester complex for building and process heat, and cleaning up the biogas and sending it to the power plant.

Evaluation factors associated with biogas and steam exchange are as follows:

Capital Cost, Maintenance Cost, Operability Alternative Description $ / KW $ / KWH Technical Risk &Reliability Exchange gas for steam at $1,400 $0.037 low high power plant

Evaluation of Biogas Utilization Technologies Table 8-2 below provides a comparison of alternative gas utilization technologies.

Table 8-2. Gas Utilization Technology Factors Estimate Capital Cost, Maintenance Technical Operability Alternative Description $ / KW Cost, $ / KWH Risk & Reliability Cogeneration $1,590 $0.015 Low Medium Induction Generator $1,600 $0.015 Medium Medium approx. Microturbines $2,800 $0.010 High Medium Fuel Cells $7,500 $0.020 High Medium Direct Fired Chiller $1,500 $0.200 Medium Medium Methanol Production Unknown - but high Unknown - but high High Unknown Exchange gas for steam at power plant $1,400 $0.037 Low High

Based on the above evaluation, as well as the Clear Spring Ranch staff's desire to further test the microturbine technology, cogeneration, microturbines, and "exchange gas for steam" are the alternatives chosen for more detailed economic analysis.

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Economic Evaluation Each of the three alternatives for gas utilization was evaluated based on a 20-year life cycle analysis. The evaluation is presented in Table 8-3, and includes capital cost, yearly operating cost, and Net Present Worth over 20 years.

Cogeneration Economics An evaluation of cogeneration was done using the following basis and assumptions:

§ All produced gas is used in the generator. § Any digester heating not provided by the generator heat recovery system will be supplied by the boilers, using diesel fuel. § 2002 gas production data is used as base year. § Calculations are based on average gas production and energy use. § All electricity produced replaces electricity that would otherwise be taken from Colorado Springs Utilities power grid at $0.025/KWH. § Natural gas costs $4/million Btu. § Energy cost (electricity and natural gas) will escalate at 4 percent per year. § Gas production will increase 2 percent per year due to increased flow to the WWTP. § 25 percent of gas heating value in generator goes to electricity, 50 percent is recovered, and 25 percent is lost. § The generator is 80 percent available. § Boiler efficiency is 80 percent.

This estimate is based on a current similarly sized cogeneration job, so the cost values used for major equipment are based on a detailed construction cost estimate. As a planning level estimate, the expectation is for +/- 25 percent with a large contingency to cover those items not identified at this level of effort.

The estimate is based on a cogeneration system using two 700 KW internal combustion synchronous generators, equipped with heat recovery equipment to be used to provide heated water to the existing sludge heating system. Also included are an allowance for improvements to the biogas cleaning system, and an allowance for improvements or additions to the building to house the new equipment.

An energy balance shows that, on average, the generator heat recovery system will provide enough heat to keep the buildings and digesters warm. Some boiler makeup using diesel fuel may be required on the coldest days of the winter.

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Operating and Maintenance costs are based on using $ 0.015 / KWH, from other similar projects by Brown and Caldwell. In the present worth analysis, we have assumed a 6 percent discount rate.

The results of the detailed cost analysis for this alternative are summarized below:

Alternative Capital Cost Yearly O&M (first year) 20-year Net Present Value Cogeneration $2,595,000 $161,000 ($1,380,000)

The NPV is negative because of the high initial investment and because the low cost of electricity to Colorado Springs Utilities results in a low value for the generated electricity.

Economics of Exchanging Biogas for Power Plant Steam Because of the proximity of the power plant, and because Colorado Springs Utilities owns both facilities, consideration has been given to an alternative where the biogas is cleaned up and sent to the power plant, and low pressure steam is returned to the digester complex to provide heating for process and buildings. The capital expenditure for the alternative is based on adding over $500,000 in gas handling and treatment improvements, and booster blowers at both ends of the pipe to the power plant. Pipelines were estimated for both steam and treated biogas, plus additional mechanical allowances for piping connections. In this alternative, O & M is based on operation and maintenance of the gas treatment equipment, power for the blowers, and $500,000 per year for preventative maintenance, repairs, and filter media replacement.

The estimate is based on an expected +/- 25 percent accuracy, and a 25 percent contingency.

The estimate is based on the following assumptions:

§ All produced gas is sent to the power plant. § All digester heating is provided by waste steam from the power plant. § 2002 gas production data is used as base year. § Calculations are based on average gas production and energy use. § The cost benefit for this alternative is based on electricity produced by the power plant valued at $0.025/KWH. § Energy cost will escalate at 4 percent per year. § Gas production will increase 2 percent per year due to increased flow to the WWTP § 30 percent of gas heating value in the power plant goes to electricity. § No cost has been assigned for the low pressure steam sent to the digester complex.

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The results of the detailed cost analysis for this alternative are summarized below:

Alternative Capital Cost Yearly O&M 20-year Net Present Value Exchange $2,470,000 $56,000 $2,555,000

Microturbine Economics An evaluation of microturbines was done using the following basis and assumptions:

§ All produced gas is used in the microturbines. § Any digester heating not provided by the generator heat recovery system will be supplied by the boilers, using diesel fuel. § 2002 gas production data is used as base year. § Calculations are based on average gas production and energy use. § All electricity produced replaces electricity that would otherwise be taken from Colorado Springs Utilities’ power grid at $0.025/KWH. § Energy cost will escalate at 4 percent per year. § Gas production will increase 2 percent per year due to increased flow to the WWTP § 30 percent of gas heating value in microturbines goes to electricity, 50 percent is recovered, and 20 percent is lost. § The microturbines are 80 percent available. § Boiler efficiency is 80 percent.

This estimate is based on information provided by Capstone on their new 60KW units, the experience of the testing currently being done, and similar items from the cogeneration estimate. As a planning level estimate, the expectation is for +/- 25 percent with a large contingency to cover those items not identified at this level of effort.

The estimate is based on twenty four (24) 60 KW Capstone units providing 1400 KW, equipped with heat recovery equipment to be used to provide heated water to the existing sludge heating system. Also included are an allowance for improvements to the biogas cleaning system, and an allowance for improvements or additions to the building to house the new equipment.

Operating and Maintenance costs are based on using $ 0.02 / KWH, based on adding to average costs form cogeneration due to conversations with the Clear Spring Ranch staff about the existing turbines. In the present worth analysis, we have assumed an 6 percent discount rate.

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The results of the detailed cost analysis for this alternative are summarized below:

Alternative Capital Cost Yearly O&M (first year) 20-year Net Present Value Microturbines $4,135,000 $257,000 $(3,388,000)

The NPV is negative because of the high initial investment and because the low cost of electricity to Colorado Springs Utilities results in a low value for the generated electricity.

Overall Comparison The three alternatives chosen for detailed economic analysis are quite different, and have resulted in very different economic values. Each alternative has some distinct advantages and disadvantages, but each qualifies as a legitimate way to utilize the biogas in a beneficial way. While avoided power generation requirements may not be of great economic consequence to Colorado Springs Utilities’ bottom line, each kilowatt of electricity generated by using biogas that would have been wasted has a positive effect on the environment and the long term world energy reserves.

The comparison of the economics of the three alternatives are presented in Table 8-3.

Table 8-3. Economic Comparison Alternative Capital Cost Yearly O&M (first year) 20-year Net Present Value Cogeneration $2,595,000 $161,000 ($1,380,000) Exchange $2,470,000 $56,000 $2,555,000 Microturbines $4,135,000 $257,000 ($3,388,000)

As can be seen by Table 8-3, sending the biogas to the power plant and using waste steam from the power plant to heat the digesters and buildings (Exchange) is clearly the financial winner. In estimating this alternative, an attempt was made to be conservative in estimating the amount of gas cleanup equipment required. The reasons the alternative was superior financially to cogeneration are:

§ Lower O&M costs - the system will have only small equipment added, with very little additional operator attention required. The O&M cost estimate includes $500,000 in materials per year for replacement of filter media and repairs. § A conversion efficiency of 30 percent was used for the power plant, compared to 25 percent for cogeneration.

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It should be pointed out that certain issues will need to be identified and worked out during preliminary design of the alternative, including:

§ The actual pressure and quality of the waste steam from the power plant. Design of the steam transfer piping will include insulation and condensate traps along the pipeline based on an energy balance for the pipeline. § Gas quality requirements and the need for a pressurized source at the power plant. The estimate includes blowers at both ends of the pipeline and new filters for removal of moisture and hydrogen sulfide, but more detail will be needed to finalize the cost. § The cost of not returning condensate to the power plant. There is a cost associated with water make-up, and, while this usage will be small compared to overall water requirement at the plant, it should be accounted for.

The biggest advantage for the "exchange" alternative is that it conforms with Colorado Springs Utilities stated goal of unattended operation. The equipment will require no regular operations adjustments, will be fully automated with alarms, and should require very little operator attention.

Recommendations This evaluation of alternative gas uses has made it clear that power generators are different than other municipalities in their energy management needs. Because of Colorado Springs Utilities low cost of electricity ($0.025/KWH), the economic analysis will usually be negative for investments. For example, if a higher electricity cost of $0.05/KWH was used, it would result in a positive NPW. For that reason, the gas exchange alternative is the only one that is viable for further consideration.

The gas exchange alternative is recommended because it has a positive economic impact on the operation, and provides a number of operational advantages to Colorado Springs Utilities:

§ The Clear Spring Ranch staff can discontinue normal operation of the boilers. Although the boilers should be retained for backup service whenever needed. The steam line from the power plant will be less maintenance intensive. § The gas cleanup equipment will involve minor additions to the current gas handling system, and the flares will be used as emergency backup only. § If properly designed, the steam heating system using waste steam from the power plant will offer an essentially unlimited supply of heating with no operation headaches. § Colorado Springs Utilities’ environmental staff will have fewer stack emissions to be concerned with.

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§ As described above, doing anything to change the current gas utilization system at the Clear Spring Ranch facility will be marginal economically. The motivation for changes, if implemented, will be based on easier operations, environmental advantages, and less waste of resources.

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Chapter 9. Environmental Evaluation

Objective The objectives of this chapter are to present and discuss environmental effects of plant processes, specifically related to air and water quality, and provide related recommendations for the SHDF. Potential future environmental effects should be accommodated by building flexibility into the facility improvements. Methods for achieving this were considered during the alternatives analysis and incorporated in the recommendations. The following items will be discussed in this chapter.

§ Water balance evaluation and groundwater levels. § Salt and nutrient considerations for management. § Air and odor control evaluation.

This chapter utilizes previously completed studies and reports and system operating data to develop an analysis of long-term environmental effects. Much of the existing water quantity, water quality, and air quality information was obtained from the 2003 Water Balance Analysis and water and from air quality data provided by Colorado Springs Utilities.

Groundwater Issues This section presents an assessment of the 2003 water-balance analysis and recent groundwater quality data associated with SHDF. The water balance and groundwater quality evaluation targeted issues related to groundwater levels in the SHDF and associated considerations for long-term nutrient and salt management in the basin that encloses the facility. The facility is located in Sand Canyon, about 11 miles south-southeast of Colorado Springs and west of Fountain Creek.

The water impoundments and supernatant handling facilities at the SHDF were originally designed based on an estimated water balance using available data for evaporation rates. The water coming to the site has been taken care of to date, but any future operational changes resulting in increased water flow may be a concern.

The recommended groundwater strategy for the future is to monitor groundwater levels and quality and to deal with any problems when they occur.

General Description of SHDF Water Management The SHDF has been in service since 1984. It was designed to stabilize, store, and dispose of the biosolids produced at the Las Vegas Street WWTF by dedicated land disposal. The SHDF also treats brine from the Zero Discharge Treatment Facility, which is a reverse osmosis system that treats blow-down water from the Ray Nixon Power Plant and recycles if back to the cooling towers. The southwest portion of the Clear Spring Ranch property is used to dispose of fly ash from the Power Plant.

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The system was designed to consume the water by evaporation from free water surfaces (FSBs, two supernatant lagoons, and the retention dam impoundment located near the mouth of Sand Canyon) and from the DLD areas. The retention dam is a compacted earth-filled structure that was designed to capture and impound all surface runoff and subsurface drainage from within the Clear Spring Ranch area. In effect, the Clear Spring Ranch property has been converted into a closed drainage basin. Some seepage through and/or beneath the dam is captured down gradient and pumped back into the impoundment. The retention dam was retrofitted with a clay slurry cutoff wall to prevent groundwater seepage beneath the dam and into the alluvial aquifer of Fountain Creek.

Each of the other SHDF structures is fully described in Chapter 3 in terms of function and capacity. Most surface water that drains into the Clear Spring Ranch area from the west and northwest is diverted around the SHDF.

Water Study Evaluation The Colorado Springs Utilities Environmental Services Department prepared the Clear Spring Ranch Excess Water Study (January 15, 2002) largely in response to rising groundwater levels in the facility area. The purpose of the Excess Water Study was to quantify the difference between all the inflows and all the outflows of the SHDF, and to identify possible measures that could be taken to correct imbalances.

Actual measurements of flow, estimates of flow (usually by subtraction), and use of simplifying assumptions are essential to the water-balance analysis, because certain flow measurements cannot be readily made or even observed. In general, most water-balance calculations are inexact. Assumptions employed in water-balance analyses are often the subject of reasonable debate by knowledgeable experts. This assessment of the Excess Water Study is no different. A summary of findings is as follows:

§ Vertical seepage (recharge) from the FSBs and especially the supernatant lagoons is not considered. § Seepage through and beneath the impoundment dam and cutoff wall is not considered. § Recharge from the DLD areas seems understated. § Recharge in non-developed areas seems overstated. § The average annual precipitation appears too high. § Lake evaporation rates or account for salinity effects on evaporation rates appears too low. § The fate and transport of the water component of the sludge separate from the organic and inorganic solids component of the sludge should be accounted for. § The basis for assigned flows of natural surface water and groundwater into the Clear Spring Ranch property is not explained.

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The Excess Water Study does not determine the rate of groundwater storage or the amount of time available before groundwater control measures must be implemented, particularly in the DLD areas. Site-specific information should be used to more accurately evaluate groundwater issues at the SHDF.

Groundwater Level Monitoring Colorado Springs Utilities routinely collects groundwater level data and groundwater samples from wells located on and below the SHDF (down-gradient to the east of the facility). According to the water-level data, since 1977 the areal extent of the retention dam impoundment and saturated alluvial aquifer has grown steadily with an increasing rate of groundwater recharge from the SHDF. The depth to the water table from the ground surface has decreased as surface water and groundwater storage behind the retention dam has increased. Groundwater levels are continuing to rise north and west of the retention dam.

The rate of water-table rise is apparently slowing or even going down in some areas, because (like a surface reservoir with gentle sloping sides) the ratio of storage volume to average head increases with increasing area of groundwater saturation in the shallow aquifer and due to the recent drought. Also, as the hydraulic gradient in the aquifer increases, the rate of groundwater flow increases. Field data indicate that groundwater levels in the vicinity of the FSBs and DLD areas are becoming shallow (within about 10 to 15 feet of the ground surface). In time, groundwater level control in this area may become a necessity to ensure the FSBs and DLD areas function properly and efficiently.

Groundwater and Process Quality Monitoring Colorado Spring Utilities monitors groundwater quality, including selected dissolved constituents (particularly nutrients and salinity) to track changes in groundwater quality both on and down- gradient from the SHDF. The water quality data generally reflect very high salinity and dissolved nutrients upstream from the dam. The groundwater quality and surface water quality up-gradient from the dam will likely continue to deteriorate. If over time, seepage from the impoundment through and/or beneath the dam increases, or if dam failure occurs, the resultant impact on downstream Fountain Creek water users and riparian habitat could be significant.

This evaluation focused on salinity and nitrate as water quality indicators. Colorado Springs Utilities measures nitrate, total dissolved solids (TDS) and conductivity at numerous locations throughout the SHDF.

Salinity. The background groundwater salinity near the SHDF appears to be on the order of 680 mg/L to 1,500 mg/L TDS (1997-2001 monitoring well data-HRMW-01), based on conductivity measurements (assuming 1,000 µmhos/cm equals 640 mg/L TDS). TDS and conductivity data indicate high levels of TDS that will continue to increase. Table 9-1 summarizes salinity data at select locations throughout the SHDF.

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Nitrate. Background groundwater nitrate concentrations are on the order of 2 mg/L (HRMW-01). Nitrate concentrations have exceeded 100 mg/L in groundwater below the process areas and above the dam. Nitrate concentrations have been detected at a range of 11 to 38 mg/L below the dam. Table 9-1 summarizes nitrate data at select locations throughout the SHDF.

Table 9-1. Water Quality Data for Salinity and Nitrate Groundwater Salinity, mg/L as Nitrate as N, Monitoring Location Sample TDS1 mg/L Background (HRMW-01) X 678 - 1,500 1.6 - 2.6 In process area and DLDs Supernatant lagoon water 2,820 - 3,240 -- Blended Sludge from Sludge Main 3,740 – 4,590 -- DLD areas near FSBs and supernatant X -- 130 - 340 lagoon (WW3A and 5A) Downgradient of DLDs and above retention X 2,520 – 6,060 180- 380 dam impoundment (SC-1) Retention dam impoundment (SCAD-2) X 3,870 – 6,300 20 - 24 Below retention dam (SCBD-4, 5 and 7) X 1,740 – 3,800 11 - 38 1 1997 to 2000 data is collected as conductivity. Conductivity measurements were converted to TDS using the conversion 1,000 µmhos/cm equals 640 mg/L TDS (Handbook of Nonpoint Pollution, Novotny, 1981).

At the Sacramento DLD sites, with much heavier biosolids application rates than at the SHDF (typically 100 dry tons/acre/year or greater at Sacramento), there has been salinity and nitrate buildup in the soils and perched groundwater beneath the site. Therefore, if biosolids application rates are increased at the SHDF DLD areas, increased soil and groundwater salinity and nitrate levels are likely. The levels within the soil have not been a problem at other DLD sites (including Sacramento) in terms of soil biota and the ability to continue to degrade the biosolids within the soil over time. The soil pH can drop somewhat over time due to organic matter decomposition. Build up of heavy metals in such DLD soils occurs over time; however, soils monitoring at the Sacramento sites (20+ years of application) shows that metals concentrations are only slightly elevated over background soil levels. Soil organic matter content has risen significantly to such DLD sites, but this has not created problems. In summary, as long as groundwater is properly contained, and adequate monitoring of the soils/groundwater situation occurs, there appears to be limited impacts from these DLD operations.

Air Emission and Odor Control Evaluations Title V of the Clean Air Act Amendments of 1990 requires major sources of air pollution to obtain a federally enforceable operating permit. The purpose of Title V operating permits is to reduce violations of air pollution laws and improve enforcement of those laws. The SHDF is co-located with several other sources of air pollution. The Colorado Department of Public Health and Environment (CDPHE) has determined that operations from these combined sources constitute a major source of air pollution. As such, the CDPHE issued operating permit number 96OPER152

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on February 1, 2001. This permit identifies limits for fuel combustion, visible emissions, emissions of pollutants as well as operating parameters.

In support of air quality compliance, the SHDF maintains data, on a daily basis, which records iron salt use, distillate oil use, digester gas use, hydrogen sulfide and sulfur dioxide production. The Air Emissions SHDF Compliance Report data recorded since July 2000 was reviewed to determine if the SHDF is currently satisfying all operating permit requirements. Some of the following information may not be applicable if the monitoring requirements are provided to CDPHE by means other than the compliance reports reviewed.

Based on review of the data provided by Colorado Springs Utilities, the SHDF is in compliance with the following specific requirements.

§ Fuel limit for digester gas and distillate oil. § Bi-weekly digester gas samples. § Annual SOx limit. § Hourly SOx limit (see Page 9-8, Air Emissions, Item 3). § Daily record of iron salt. § Hydrogen sulfide concentration results are maintained. § Annual NOx limit. § Annual VOC limit. § Annual CO limit. § Annual PM10 limit. § Annual PM limit.

The data that is contained within the compliance reports indicated that the SHDF is in compliance with the operating permit for emission limits of these pollutants.

The following information could not be verified from the provided compliance reports:

§ PM emissions of 0.21 pounds per MMBtu per boiler. § Monthly totals of PM emissions (used to calculate 12-month rolling total). § Monthly totals of PM10 emissions (used to calculate 12-month rolling total). § SOx emissions of 0.8 pounds per MMBtu per boiler. § SOx emissions of 0.5 pounds per MMBtu per boiler. § Monthly totals of NOx emissions (used to calculate 12-month rolling total). § Monthly totals of VOC emissions (used to calculate 12-month rolling total). § Monthly totals of CO emissions (used to calculate 12-month rolling total). § Vendor supplied distillate oil sulfur content. § Records of biogas released due to malfunction. § Records of adjustment and preventative maintenance of iron salt flow meter. § Records of monthly Method 22 surveys for biogas flares. § Hours of operation (used to calculate hourly SOx emissions). § Annual fugitive VOC and HAP emissions.

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This information is based on the new anaerobic digestion complex having operated for more than 12-months, thus removing the requirement to provide hourly or monthly compliance demonstration for all pollutants except oxides of sulfur, which still has an hourly limit. Additionally, records of any opacity surveys (Method 22) or observations (Method 9) are not contained within the compliance reports.

On July 31, 2003 the Colorado Air Pollution Control Division (APCD) conducted a field inspection at the Clear Spring Ranch facility. The facility received the following comments:

§ Operating hours and fuel oil sulfur content were not included in the provided information in order to verify SO2 hourly emission estimates. Future inspections should more closely investigate hourly emission estimates. (Requirements 2.6 and 2.8) § Future inspections should identify sample analysis method(s) used for bi-weekly samples of digester gas. (Requirement 2.7) § The SHDF did not submit its Semi-annual Monitoring Report by the due date of September 1, 2002. The APCD received this report on September 3, 2002. The source was advised to submit all reports prior to their due date. No further action is recommended. (Requirement 7)

In addition, the following recommended permit revision for future inspections was made by the APCD:

§ Clarify whether average H2S concentrations is used in emission calculations (see Appendix H of the permit).

Odor Control Colorado Regulation No. 2 Odor Emissions identifies odor limitations applicable to the SHDF. Part A General Provisions limits areas that are not residential or commercial to odors which are not detectable after the odorous air has been diluted with fifteen (15) or more volumes of odor free air. There are no requirements to demonstrate compliance with this regulation. However, this is primarily a nuisance regulation that does not include testing requirements until a complaint is filed. Currently the SHDF utilizes a biofilter at the wetwell prior to digestion.

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Recommendations The following recommendations are intended to facilitate sustainable operation and management.

Water Management Plan Better water management will help increase evaporation while improving groundwater quality. The following recommendations were developed to help decrease the inflow and/or increase the outflow of water to the SHDF system.

1. A groundwater drainage plan for selected FSBs and DLD areas should be developed. Such a plan should be based upon site-specific hydraulic properties of the geologic materials to be drained. A hydrogeologic investigation is needed that should include drilling and testing of wells. Future groundwater control options include:

§ Line the supernatant lagoons with a clay or plastic liner to prevent seepage, § Install dewatering wells, and § Install horizontal drains near selected FSBs and DLD areas.

2. Based on information developed previously (Excess Water Study, etc.), the probable need for increased sludge flowrates, and making even optimistic assumptions about improved DLD evaporation, it seems likely that there is a need for an excess water handling system at the SHDF as outlined in Chapter 6. The least cost way to handle such excess water would probably be beneficial use on-site through a crop irrigation system. Therefore, evaluation work should proceed to site such an irrigation system, define crops consistent with excess water characteristics, and determine facilities size and related requirements and costs. Other excess water handling alternatives at SHDF may also need to be updated (such as treatment and creek discharge) so that cost comparisons with an on-site irrigation system can be identified.

3. The level and quality of the groundwater at the SHDF must be monitored to determine if problems are developing. The ability to beneficially reuse the excess water from the facility in the future will be critical to long-term success.

Other Water Treatment Options Other sustainable treatment options are available that should be considered for both economic and environmental reasons.

1. If a new wastewater reclamation facility is built at or near the SHDF location, excess water from the Clear Spring Ranch site could be treated and discharged through the plant’s discharge permit.

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2. The water that is transported to the SHDF as sludge is equivalent in volume to the yield from one or two Denver basin wells in the city. This water is 100% reusable (trans-basin, consumptive use, and/or nontributary groundwater) by volume. The value of this water likely ranges from $300 to $500 per acre-foot (as treated water), which could be used by Colorado Springs Utilities for augmentation, exchange, direct sale, lease, or enhancement of minimum streamflows. Colorado Springs Utilities should determine the potential value of this water as treated for these and/or other potential uses. This value should then be compared with the cost to treat the water for direct discharge into Fountain Creek.

Air Emissions

1. Colorado Springs Utilities should ensure that all operating permit compliance requirements are provided to CDPHE, if not already doing so.

2. If Colorado Springs Utilities has data not provided in the compliance reports (such as maintenance or operator records), this data should be organized in the event that it is required in the future.

3. It appears that Colorado Springs Utilities tracks hourly SO2 emissions. The operating permit allows the utility to divide the daily emissions by the hours of operation. Therefore, CDPHE allows hourly exceedances if the facility does not exceed the daily average based on the hours of operation. Current reporting may be more conservative than is required.

4. Investigate using a database system to manage data, if this is not currently done. This can assist in identifying exactly what data is required and enable printing reports of exactly what is required.

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Chapter 10. Siting and Landscape Architecture Planning

Introduction The objective of this chapter is to consider siting and landscape architecture planning for the five potential alternatives at the SHDF. General areas will be identified for future process considerations. In addition to the potential expansion of existing processes and incorporating new processes, such as thickening, the Lower Fountain Water Reclamation Facility (LFWRF) could possibly be located at the Clear Spring Ranch site. This chapter also includes consideration of architectural issues relating how new facilities will be built to fit in with the existing structures, and the use of excess water from the proposed thickening and dewatering operations to implement landscaping to the site.

History The Clear Spring Ranch site was developed from the Hanna Ranch, which was acquired by Colorado Springs Utilities in 1972. Colorado Springs Utilities purchased the land and has constructed the Nixon Power Plant, the Zero Discharge Water Treatment Plant, the SHDF, and the recently completed Front Range Power Company power plant. A containment dam was constructed to prevent water from the SHDF and other activities at the site from escaping into other drainages and to Fountain Creek. The site has been used as a solids treatment and disposal facility since 1978, and has functioned successfully and cost effectively in that capacity. Because of being located away from developed or occupied areas, little consideration to landscaping and architecture has been needed to date. This solids facility Masterplan provides direction for new construction and changes to the facility over the next twenty-five years. Figure 10-1 shows the existing SHDF site plan.

Future Considerations Because of the expectation of significant new construction at the SHDF, and because there will be future development in the area that will make layout and appearance more important, a conceptual site plan has been developed showing probable locations for future improvements. These locations will be finalized and better defined during preliminary design for each of the planned improvements, but this plan provides general guidelines for layout and related features.

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Figure 10-1. Existing SHDF Site Plan

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Locations for Improvements The following sections describe the potential locations of components associated with the five alternatives.

Raw Sludge Thickening Raw sludge thickening is recommended for Alternatives 1 through 4, but is not necessary for Alternative 5.

Adding thickening prior to the digestion process at the SHDF is desirable for several reasons:

1. To allow reduced sludge residence time in the pipeline by pumping thinner sludge, 2. Reduce the number of digesters that need to be operated in the near-term and long term, 3. Cut sludge heating requirements as a result of reduced digester feedrates, and 4. Delay the time that additional digesters would need to be constructed.

A thickening system at the SHDF is recommended in a new structure (concrete building approximately 80 feet x 80 feet) near the current Sludge Main discharge point and adjacent to the digesters. The system would consist of three thickening centrifuges with feed pumps, polymer system, power supply, control systems, odor control, etc. In addition, a thickened sludge storage/mix tank and thickened sludge pumping facilities are recommended. For the RFBB alternative (Alternative 5), raw sludge dewatering facilities would be located at the Power Plant unless the thickening system is in place, in which case the thickening system would be converted to raw sludge dewatering.

The proposed location of a raw sludge thickening facility is displayed on Figure 10-2 near the wetwell and anaerobic digesters.

Raw Sludge Dewatering In Alternative 5, the raw sludge from the pipeline is dewatered prior to feeding to a proposed RFBB.

For the purposes of this Masterplan, it has been assumed that a new pipeline would be extended from the existing pipeline to the power plant. A dewatering facility would be built at the site of the RFBB, which would dewater the sludge slurry to about 20% solids, and the cake would be conveyed directly into the RFBB. For the purposes of this study, centrifuge dewatering was assumed rather than belt presses.

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Figure 10-2. Proposed Improvements

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In general, the system would be designed to be implemented in two phases; the first phase to be built in the near future and sized to provide service through the year 2015, and a second phase to be operational in 2015 that would have capacity through at least the year 2025.

A dewatering system is assumed to be within a new concrete building sized for 3 centrifuges and 2 cake storage tanks. The size of the building to hold the centrifuges and related equipment is estimated to be about 100 feet x 80 feet.

The location of raw sludge dewatering is displayed on Figure 10-3 at a proposed site at the Nixon Power Plant. The actual site location will need to be reviewed and coordinated with the RFBB installation and location. However, if thickening is installed and converted to dewatering in the future (see Chapter 11), the location will be as shown for the thickening system (Figure 10-2).

The centrate from the dewatering operation would be treated before being introduced to the existing FSBs for further treatment. At least for the initial few years, the digesters would remain partially functional, to provide a backup sludge treatment method, and to provide an active microbial environment in the FSBs to help treat the centrate.

An Upflow Anaerobic Sludge Blanket Reactor is recommended as the centrate treatment system. This system consists of a reactor vessel, biogas handling system, and associated equipment. Treated centrate would flow into the FSBs where it would receive additional biological treatment, and FSB supernatant would flow into the supernatant pond. A pump station and chemical treatment system would be used to pump and spread this water for irrigation on about 300 acres of land on the Clear Spring Ranch site. If the LFWRF is constructed at Clear Spring Ranch, then a separate centrate treatment system is not necessary.

The proposed location of the centrate treatment facility is displayed on Figure 10-2 adjacent to the FSBs at the SHDF. The irrigation pump station will be located near the supernatant ponds as shown on Figure 10-2.

Digested or Harvested Sludge Dewatering In Alternatives 1 through 4, dewatering of digested or FSB-harvested sludge is used in the future to improve the capacity of the FSBs, the DLDs, or as a pretreatment for additional treatment, such as for sludge drying. Dewatering reduces the moisture content of digested sludge so that it has a semi- solid consistency ranging from 15 percent to 40 percent dry solids. Sludge dewatering reduces hauling costs and disposal costs related to volume. It also is a prerequisite of many post-treatment processes.

Initial screening of dewatering technologies revealed that belt presses or centrifuges would be used, depending on the alternative recommended.

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Figure 10-3. Potential Raw Sludge Dewatering Location For RFBB Alternative

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The proposed location of sludge thickening (of either digested or FSB-harvested sludge) is displayed on Figure 10-2 between the digesters and FSBs.

FSB Expansion In Alternatives 1 and 3, additional FSBs are required to expand the existing system to meet future capacity needs under the design FSB loading rate of 20 lbs. VS / 1,000 ft2 / day. Two additional FSBs are recommended to accommodate the 2025 projected loading based on the Colorado Springs only projected loadings and seven additional FSBs are recommended to provide adequate capacity based on County 2025 projected loading.

For the two additional FSBs included for the City-only projections, the proposed location is north of the exiting FBSs. For an addition of seven new FBSs, the proposed location is both north and south of the FSBs as shown on Figure 10-2.

DLD Expansion In Alternative 1 City-based projections, it is assumed that tillage will increase evaporation, therefore no additional DLD area is needed. For the County-based projections, it is assumed that applying dewatered cake by spreading it and incorporating it into the soil would be sufficient to meet the higher application rates. An additional 64 acres would be required for the DLD system (County- based projections) in addition to the 36-acre expansion expected in 2004.

There are several areas identified on Figure 10-1 that indicate areas reserved for future DLD. These areas were determined by Colorado Springs Utilities staff and obtained from the 2002 Colorado Springs Utilities staff report titled “Preliminary Report – Clear Spring Ranch Excess Water Study”.

Heat Drying Alternative 2 includes heat drying of digested, dewatered sludge to produce Class A material for beneficial use options. Various thermal drying systems could be used at the SHDF. A heat drying operation includes the heat drying equipment, a building, sludge storage, product storage, and ancillaries including substantial air pollution control equipment. The building (approximately 15,000 s.f.) will house the drying facilities and equipment. In addition, dry final product storage on-site in silo-type facilities for truck loadout is needed.

The proposed location for the heat drying system at the SHDF is displayed near the proposed dewatering facilities on Figure 10-2.

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Air Drying Alternatives 3 and 4 include air drying (during warm seasons) to produce a Class A product. Air drying operations would require the addition of paved drying beds and acquisition of mechanical equipment to mix and move the material. Stockpiling of the product is easily accommodated with air-dried product, and such stockpiles are easily sampled for Class A pathogen-density determinations.

Alternative 4 assumes dewatering a portion of the digested slurry. Based on City and County-based projections, 20% to 50% of the flow, respectively, would be air dried in order to avoid constructing additional FSBs and DLD in the future.

Year 2025 FSB production is estimated to be 9,000 dry tons/year and 13,000 dry tons/year for City and County-based projections, respectively. This production would require approximately 30 to 43 acres of paved cake drying beds for City and County-based projections, respectively.

The proposed location for the air drying beds at the SHDF is shown immediately south of the existing FSBs on Figure 10-2.

Appearance of New Buildings

Basic Criteria Depending on the selected alternative, the following potential new buildings and/or treatment processes could be recommended for implementation at the SHDF:

§ Thickening § Additional FSBs § Additional DLD acreage § Dewatering § Centrate treatment system § Heat drying § Air drying

It is recommended that, as part of the preliminary design for the first of the new capital projects at this site, an architectural and landscaping plan be developed, so any new construction is properly planned. The new plan would address geotechnical and structural issues and standards as well as setting parameters for layout, traffic, parking and aesthetic issues. The landscaping plan would designate the layout and standard for vegetation appropriate for the site, and would identify future landscape features so that new facilities can be built to conform.

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Lower Fountain Water Reclamation Facility The Lower Fountain Water Reclamation Facility (LFWRF) is a proposed wastewater treatment facility currently being planned for the southern Colorado Springs Metropolitan Area to treat flows from the Jimmy Camp Creek Basin. The following information on the LFWRF siting was obtained from an ongoing study (MWH, August 18, 2003 Memorandum RE: Lower Fountain Regional Water Reclamation Facility Siting Study).

Proposed Location Initially, six potential sites were evaluated as a part of the study. An economic and noneconomic comparison was completed and the six sites were reduced to the three most feasible sites. The remaining three sites were investigated further. Results of the evaluation indicated that the Clear Spring Ranch area is the most favorable location for the LFWRF. Figure 10-4, obtained from the August 18, 2003 Siting Memorandum (“Figure 3”), displays the location of the proposed LFWRF at Clear Spring Ranch.

Interceptors would be built to bring wastewater from the east and west sides of the Colorado Springs metropolitan area, and a reclaimed water pipeline would be built to Williams Creek Reservoir at a later date.

Irrigation and Landscaping Chapter 6 describes the potential increase in the quantity of water at the site created by sludge thickening (and because of increased flowrates recommended for the Sludge Main). This increased flow of water to the site, if not handled appropriately, would cause a significant increase in the already observed increase in site groundwater levels, and would eventually disrupt operations in the DLDs and cause concerns of contamination of nearby aquifers.

Water Availability The centrate generated during thickening and the filtrate or centrate produced from dewatering will need to be prevented from building up in the groundwater. The water generated from thickening or dewatering must be treated before the water can be used elsewhere. After treatment, the centrate or filtrate could be conveyed to the FSBs, where additional biological treatment occurs naturally. The water from these operations eventually flows to the supernatant ponds.

The excess flow to the supernatant ponds can be handled by building an irrigation system consisting of a pump station, hypochlorite dosing equipment, and a piping and spray system to apply the water. The TDS levels in the water will be fairly high, possibly restricting the types of vegetation that can be used.

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Figure 10-4. “Figure 3” From MWH, Memorandum RE: Lower Fountain Regional Water Reclamation Facility Siting Study, August 18, 2003

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About 300 acres (assuming 20 inches per year net evaporation rate) of land would eventually be needed at Clear Spring Ranch to dispose of the excess water. There is approximately 1,500 acres available due east and southeast of the SHDF (located on both the east and west side of Interstate 25) within the Clear Spring Ranch Property Boundary that could possibly be used for rangeland or crop irrigation.

Regulatory and Health Issues The quantity of centrate flow totals between 400 and 600 acre-feet per year assuming a Sludge Main flow of about 0.70 mgd. Following anaerobic treatment, estimated centrate characteristics are shown in Table 10-1. Also shown in Table 10-1 are estimated characteristics if this treated centrate is discharged through the FSBs and then becomes FSB supernatant stored in the Supernatant Lagoons. Either stream (treated centrate or FSB supernatant) then needs to be handled in some manner for final treatment or use/disposal. It is believed that this water from the supernatant ponds could be used for either crop or landscape irrigation, as long as primary contact is prevented.

Table 10-1. Estimated Excess Water Characteristics Treated Centrate from FSB Supernatant-Probably from Parameter Sludge Thickening Supernatant Lagoons Flowrate 0.35 to 0.5 mgd (400 to 600 acre-feet annually) 0.25 to 0.40 mgd (300 to 450 acre-feet annually)a Susp. Solids 200 to 500 mg/L 150 to 300 mg/L BOD 200 to 500 mg/L 200 to 300 mg/L PH ~7.0 ~7.5 Ammonia-N 200 to 400 mg/L 200 to 250 mg/L

PO4-P 50 to 250 mg/L 100 to 200 mg/L TDS 2,000 to 3,000 mg/L 2,000 to 3,000 mg/L a This would be extra FSB Supernatant over and above what is currently produced. Notes: 1. Further testing is required to refine these estimates. 2. Excess water can be taken as treated centrate or FSB Supernatant. So, excess water is one or the other, not both.

Site Land Use Planning Various options were identified in Chapter 6 for handling of excess water from the supernatant ponds. The most feasible options identified at this time for handling and processing the excess water are the following:

§ Irrigation at Clear Spring Ranch using this water to grow a crop or landscaping (growth of poplar trees was evaluated in 1998, but other crops can be considered). § Use of irrigation and natural features to create a wildlife habitat on the Clear Spring Ranch property.

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§ Treat at proposed LFWRF and discharge to Fountain Creek or reuse water. This alternative is attractive due to the augmentation requirements on Fountain Creek, and because mixing supernatant with treated wastewater will reduce the TDS levels in the irrigation water, making it less restrictive for crop irrigation.

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Chapter 11. Recommended Alternative for Future Facility Improvements

Introduction The objective of chapter is to develop a list of recommended facility improvements that will meet the needs of Colorado Springs Utilities in the future based on the analysis of the preceding tasks and chapters. Recommendations for facilities and equipment are based on projected solids loading through 2025 and on associated capacity requirements and are prioritized according to the order in which capacity concerns or other bottlenecks are expected.

The recommended system is Alternative 1 and includes expanding/modifying the existing solids handling, treatment, and disposal facility at Clear Spring Ranch and proposes a new thickening facility. Figure 11-1 (schematic) and Figure 11-2 (site plan) illustrate the components of the recommended improvements.

Chapter 7 (Alternatives Evaluation) considered factors such as economics, reliability, ease of operation, and flexibility in the selection process. Project costs included in this Chapter have been refined since completion of Chapter 7 for the recommended system (Alternative 1) only. Annual O&M costs have not changed.

Throughout this Masterplan, both City-wide and County-wide projections were used as a basis for the evaluation. This chapter provides recommendations only for the City-based projections and the current study area. Since Alternative 1 is an expansion of the existing system, it will allow for conversion to other process options should the solids loading or regulatory requirements change in the future. Chapter 7 revealed that for the County-based scenario, Alternative 5 (RFBB) is the most economically feasible alterative. Should the RFBB be installed in the future (approx. 2008) and/or if the service area increases, and/or if other assumptions or economic factors change significantly, the improvements made for Alternative 1 can be modified to meet the Colorado Springs Utilities’ needs. For example, the thickening system can be modified and converted to a raw sludge dewatering system prior to feeding a RFBB.

The locations identified in Chapter 10 (Siting and Landscape Architecture Planning) for additional processes for the five alternatives were developed for planning purposes only. The design assumptions and criteria must be further investigated when the design for the improvements is implemented. Although the final design features may depart from those described below, the proposed improvements outlined are representative of those needed by Colorado Springs Utilities and should be adequate to be used for long-range planning and financing purposes.

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Figure 11-1. Alternative 1 – Modified or Improved FSB/DLD System

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Figure 11-2. Alternative 1 Recommended Improvements

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Recommended Existing System Improvements Based on the evaluation conducted and summarized in Chapter 7, Alternative 1 is recommended as the preferred solids handling, treatment, and disposal management system for projected City-based loadings. The alternative includes the addition of thickening prior to digestion and expansion/ modification of the existing system. Alternative 1 (City-based) has a lower present worth cost than the other alternatives as shown in Chapter 7. Implementation of Alternative 1 is essentially divided into the following areas:

§ Grease Handling Improvements (this improvement was added after the initial evaluation in Chapter 7). § Sludge Thickening/Centrate Treatment. § Digestion Modifications. § FSB Expansion. § Improvements to the DLD System. § Water Management/Irrigation.

Each of the above-listed proposed projects are briefly described below. Chapter 12 provides detailed project information sheets describing each of the proposed projects.

Grease Handling Improvements The existing grease/scum handling system for the material from Las Vegas Street WWTF includes collection in a heated concentrator and transfer to a unheated tanker truck. When the truck is full, the congealed grease is transported to the SHDF, where the truck is heated to liquify the grease. When the grease is liquid, it is quickly transferred into the digesters, causing a surge in gas production.

The recommendation for this system includes a new tanker truck, with provisions to allow a slow transfer of liquid grease. Also, provisions should be made at the Las Vegas Street WWTF to apply steam or hot water to the tanker’s heating coils. If the grease is kept warm, it can be transferred starting immediately at the SHDF. At Clear Spring Ranch, provisions will be made to transfer grease at a measured rate. Also, the ventilation must be improved in the SHDF grease building to protect worker health.

Raw Sludge Thickening/Centrate Treatment Raw sludge thickening is recommended at the SHDF. Adding thickening prior to the digestion process is desirable for several reasons:

§ To allow reduced sludge residence time in the pipeline by pumping thinner sludge,

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§ Reduce the number of digesters that need to be operated in the near-term and long term, and § Cut sludge heating requirements as a result of reduced digester feedrates.

Pilot testing is recommended for the proposed sludge thickening process. Both centrifuges and GBTs should be pilot tested.

For planning purposes, thickening centrifuges are the recommended process due to the characteristics of the solids arriving at the SHDF (fermented, low pH, and extremely odorous), therefore the thickening process would need to be fully contained. In addition, thickening centrifuges can be converted to function as dewatering centrifuges, but this should be investigated further and discussed during the pilot testing. This conversion would allow dewatering capability should a RFBB be installed in the future at the Ray Nixon Power Plant. In addition, centrifuges are recommended for this application because of odor considerations and the ability of centrifuges to operate unattended or with minimal attention in a 24 hour per day/7 days per week operating mode. Although centrifuges are recommended in this study, Colorado Springs Utilities should also perform pilot testing and further evaluate the use of GBTs.

The thickening system would be contained in a new structure (concrete building approximately 90 feet x 80 feet) near the current Sludge Main discharge point and adjacent to the digesters. From the Sludge Main discharge, the flow would be diverted and flow by gravity to new raw sludge storage tanks with mixing capability and then pumped to new thickening centrifuges. After thickening, the sludge would be pumped to either the new thickened sludge storage tanks or directly to the existing wetwell, with added mixing. The thickened sludge will then be pumped to the existing digesters. The thickening system would consist of three thickening centrifuges with feed pumps, a polymer system, power supply, control systems, odor control, thickened sludge storage/mix tanks, and thickened sludge pumping facilities.

An upflow anaerobic sludge blanket reactor is recommended for centrate treatment. The centrate would be pumped through a packaged, skid mounted system. The process would consistently remove high levels of COD and nitrogen compounds before the treated centrate flows to the FSBs for polishing. These systems are widely used in the ethanol production industry, and produce useful amounts of biogas.

The LFWRF is a proposed wastewater treatment facility currently being planned for the southern Colorado Springs Metropolitan Area to treat flows from the Jimmy Camp Creek Basin. Preliminary results of the ongoing Siting Study indicated that the Clear Spring Ranch site is the most favorable location for the LFWRF. Should this new WRF be constructed at the Ranch, separate treatment would not be necessary to treat the centrate produced from the thickening centrifuges. A cost savings of probably $2,700,000 may be possible if the upflow anaerobic sludge blanket reactor is not needed.

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Digestion Modifications At some time in the future, depending on the condition of the equipment, conversion of the four existing digester covers to submerged-fixed type and from an unconfined gas lance system to a mechanical draft tube mixing system is recommended. A structural integrity review of the digesters should occur to determine the need for the cover replacement, mixing, and structural improvements. This modification is recommended to prevent the floating covers from causing problems as they age, for foam control, to have automated mixing control, and increased reliability. Although recommended for planning purposes, Colorado Springs Utilities may wish to further evaluate as additional experience is gained.

Colorado Springs Utilities plans to take an older digester off line next year and clean it out to determine its struvite situation. The large amount of material discovered in Digester 7 in 2003 was determined (through testing) to be almost entirely struvite.

It is recommended to perform a pilot test to add iron chloride at the Las Vegas Street WWTF BSPS for struvite control. Colorado Springs Utilities staff are continuing the phosphate and related testing of sludge and should have results to help confirm if phosphate solubilization during Sludge Main travel is the likely cause of the extraordinary struvite scale deposits in the digesters. After pilot testing iron chloride addition at the BSPS, and with the latest data available, Colorado Springs Utilities should revisit the struvite problem and solutions.

FSB Expansion In order to remain under the design FSB loading rate of 20 lbs. VS / 1,000 ft2 / day, two additional FSBs are recommended (total of 11). The proposed location of the proposed two units is north of the existing FBSs. It is also assumed that the dredge will need to be rehabilitated during the planning period.

In addition, it is recommended Colorado Springs Utilities develop procedures for determining the amount of solids within each FSB. This is important for various operational reasons including: (1) need to know if basin is full – overfilling the basin creates odors, and difficulty in floating the dredge; (2) need to plan for future dredging operations, to insure that too many basins do not reach “full” status during the same year; (3) need to monitor the thickness of sludge within basins to confirm basin health and inventory status; and (4) determine if dredging activity has removed the planned quantity of solids.

Improved and Modified DLD System It is assumed that tillage on the DLD acreage will increase evaporation and the current application rate of 7 inches/year.

Testing should be performed to determine appropriate tillage schedule and determine target increased evaporation rates.

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Therefore, no additional DLD acreage is recommended. Costs for equipment (tillage) have not been included in the capital cost estimate. It is assumed that tillage costs would be included under annual O&M costs.

One TerraGator should be added during the planning period.

Water Management The centrate generated during thickening will need to be prevented from building up in the groundwater. The water generated from thickening must be treated before the water can be used elsewhere. After treatment, the centrate or filtrate could be conveyed to the FSBs, where additional biological treatment occurs naturally. The water from these operations eventually flows to the supernatant ponds.

Various options were identified earlier for handling of excess water from the supernatant ponds. The most feasible options identified at this time for handling and processing the excess water are the following:

§ Irrigation at Clear Spring Ranch using this water to grow a crop or landscaping (growth of poplar trees was evaluated in 1998, but other crops can be considered). § Use of irrigation and natural features to create a wildlife habitat on the Clear Spring Ranch property. § Treat at proposed LFWRF and discharge to Fountain Creek or reuse water. This alternative is attractive due to the augmentation requirements on Fountain Creek, and because mixing supernatant with treated wastewater will reduce the TDS levels in the irrigation water, making it less restrictive for crop irrigation. § Use water for power plant cooling water. § Sell water to nearby users (gravel quarry).

At this time and for purposes of cost planning, it is assumed that an irrigation system at Clear Spring Ranch will be implemented.

Groundwater collection through an exfiltration system, a perforated pipe installed below the groundwater level, is recommended as a contingency to be used if groundwater levels rise. The permeability and water production characteristics of the soils in the area needing treatment would be investigated prior to designing the groundwater removal system. Excess groundwater could be disposed of by pumping to the Nixon Power Plant to be used as cooling water.

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Sludge Screening at Las Vegas Street WWTP BSPS Sludge screening at the Las Vegas Street WWTP BSPS is recommended but would more logically be defined in the Las Vegas Street WWTP Masterplan. This project will affect some of components at the SHDF. Because of the need for raw sludge to pass through centrifuges for Alternative 1, it is recommended that the raw sludge be screened before it leaves the Las Vegas Street WWTF. Screening will eliminate concerns about plugging the centrifuges, as well as removing the “trash” from the FSBs and digesters.

In addition, if biosolids products are produced in the future for off-site use, sludge screening to reduce debris content must be undertaken. The Parkson Strainpress has a good history of removing such debris. Normally it is used with 5 mm perforated screens on thickened primary sludge. It is possible that this type of process could be implemented at the Las Vegas Street WWTP on the thickened or semi-thickened primary sludge. Such a screening system would need to have two units and have associated sludge feed systems, screenings handling/loadout, odor control, and related systems. A new or modified structure would be required.

Timing of Improvements An implementation plan and schedule is provided in Chapter 12, which also includes the CIP and financial plan for the recommended improvements described herein. The following is a general list of improvements and estimated timing based on order in which bottlenecks will be experienced, based on projected loadings. A more detailed phase-in of improvements is included in the CIP and financial plan to ensure that capacity needs are met on a timely basis. The timing of some of the projects is dependent on study or pilot test results.

§ Grease Handling Improvements – 2006. § Sludge Thickening/Centrate Treatment – 2006/2007. § Water Management – 2006. § Improvements to the DLD System – 2006. § FSB Expansion – 2010. § Digestion Modifications – 2015 (timing depends upon equipment condition).

Refined Capital Costs Table 11-1 summarizes the components, descriptions, and estimated capital cost of the recommended system. The cost figures in Table 11-1 are total project costs and include allowances for predesign, design, bidding, construction, contingency, construction management, start-up, and administration costs. All of these costs are stated in terms of year 2003 dollars.

In addition, the cost presented in Table 11-1 have been provided at a greater level of detail than in Chapter 7. Each recommended improvement has been broken down into several components. Construction contingency remains at 30 percent, which includes two components, “unidentified due to planning level” and “risk factor”, each at 15 percent. Engineering, legal, and administration was reduced from a factor of 25 percent to 18 percent since Colorado Springs Utilities will not require

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legal services for coordination of construction with the local governmental agencies, land purchase, easement, right-of-way transactions, special investigations, surveys, foundation reports, and location of interfering utilities. This factor of 18 percent has been used to allocate 10 percent for design and 8 percent for construction services. Appendix C provides detailed cost information for each of the recommended improvements.

Table 11-1. Alternative 1 Estimated Total Project Cost Component Total Project System Total Project Cost, Cost, Component Description Unit Cost Dollars Dollars Grease Handling Improvements: Tanker truck 1 unit $100,000/unit $153,000 Heating System Located at Las Vegas Street WWTF $50,000 LS $77,000 HVAC Improvements Located at Grease Building $75,000 LS $116,000 Total Grease Handling Improvements $346,000 Sludge Thickening / Centrate Treatment Sludge Thickening: Diversion/bypass structure to Pipeline route raw sludge to thickening system $250,000 LS $384,000 Raw sludge 2 @ 75,000 gallons inside storage tank building $2.50/gallon $576,000 Sludge storage 32' dia x 8" thick cast concrete, 2 tank bottom tanks, 50 cu.yd. $300/cubic yard $24,000 Centrifuge feed Centrifugal, 500 gpm each, 3 pumps pumps $17,000/unit $78,000 Alfa-Laval, ALDEC 706G2, 3 Centrifuges units $600,000/unit $2,761,000 Polymer addition tank 1 unit $15,000/unit $24,000 Polymer pump 2 unit $3,000/unit $9,000 Polymer pump -- Controls LS $2,000 LS $4,000 Polymer pump-- Miscellaneous LS $5,000 LS $8,000 Thickened 10,000 gal each, hopper bottom sludge storage with steel legs, 2 tanks $5 /gallon $153,000 Thickened sludge mixing improvements Retrofit wetwell $100,000 LS $153,000

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Component Total Project System Total Project Cost, Cost, Component Description Unit Cost Dollars Dollars Thickened sludge feed Centrifugal, 120 gpm each, 3 pumps pumps $10,000/unit $46,000 Cast in place floors – 250 yards $250/yard $97,000 Cast in place walls – 400 yards $400/yard $245,000 Pads curbs, etc. – 10 yards $200/yard $4,000 Twin T roof –7,500 s.f. $13/s.f. $150,000 Building Electrical and mechanical–7,500 s.f. $17/s.f. $196,000 Architectural finish–7,500 s.f. $20/s.f. $230,000 Structural excavation and backfill–5,000 yards $10/yard $77,000 Process piping 2,000', 8-inch average, on hangers $60/linear foot $184,000 3,000', 8-inch average, buried 5' Yard piping deep $80/linear foot $368,000 Thickening odor control 14,000 cfm to Biofilter $45/cfm $966,000 Plant electrical service LS $900,000 LS $1,381,000 Sitework 10,000 yards $6/yard $92,000 Bridge crane Equipment maintenance $200,000 LS $307,000 Miscellaneous steel Stairs, ladders, platforms-15 tons $3,000/ton $70,000 Subtotal – Sludge Thickening $8,587,000 Centrate Treatment: Packaged system, upflow Centrate anaerobic sludge blanket reactor, Treatment 2 units $750,000/unit $2,301,000 Ancillary Concrete pad, piping equipment connections, utilities, installation $250,000 LS $384,000 Subtotal – Centrate Treatment $2,685,000 Total Sludge Thickening / Centrate Treatment $11,272,000 Irrigation System: Irrigation pump 500 gpm, bleach injection, house floating pond intake, 3 pumps $250,000 LS $384,000 Irrigation piping 2 miles of 8-inch DI pipe $50/linear foot $809,000 Spray equipment $150,000 LS $230,000 Total Irrigation System $1,423,000

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Component Total Project System Total Project Cost, Cost, Component Description Unit Cost Dollars Dollars FSB Expansion: Excavation 60,000 yards per FSB, 2 FSBs $3/yard $552,000 Lining 270,000 s.f. per FSB, 2 FSBs $2.50/s.f. $2,072,000 8-inch gravel layer on liner 5,400 yards per FSB, 2 FSBs $10/yard $166,000 bottom

Concrete ramp 16 yards per FSB, 2 FSBs $250/yard $12,000 Concrete structures 20 yards per FSB, 2 FSBs $400/yard $24,000 Mechanical equipment 2 FSBs $100,000/unit $306,000

Piping 1,500 feet per FSB, 2 FSBs $75/linear foot $345,000

Electrical LS $50,000 LS $154,000

Total FSB Expansion $3,631,000 Digestion Modifications : Concrete 350 yards per Digester, 4 units $700/yard $1,504,000 Mixing equip 4 mixers per unit, 4 units $80,000/mixer $1,964,000 New pumps 3 pumps/digester, 4 units $20,000/pump $368,000 Heat exchanger, pump, valves, New heat loop etc., 4 units $150,000/unit $920,000 Modifications – gas and process, Piping 4 units $100,000/unit $612,000 Electrical, Controls 4 units $150,000/unit $920,000 Building/HVAC modifications 4 units $150,000/unit $920,000 Total Digestion Modifications $7,208,000 FSB/DLD Equipment: FSB Dredge Rehab Dredge rehab $125,000 LS $125,000 DLD Equipment One TerraGator $225,000/unit $230,000 Total FSB/DLD Equipment $355,000

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Component Total Project System Total Project Cost, Cost, Component Description Unit Cost Dollars Dollars Studies and Testing: Pilot Test Iron Chloride at BSPS for Struvite Control $200,000 Sludge Thickening Pilot Tests (Centrifuge and GBTs) $250,000 Study to Evaluate Aquifer Production Capability $80,000 Structural Integrity Review of Digesters 1 to 4 $20,000 DLD Tillage Testing/Field Trials $100,000 Total Studies and Testing $650,000 TOTAL PROJECT COST FOR ALTERNATIVE 1 $24,885,000

Annual O&M Costs Table 11-2 summarizes the components and estimated annual O&M costs of the recommended system. These costs are stated in terms of year 2003 dollars.

Table 11-2. Projected Annual O&M Costs (dollars/yr) Component Annual O&M Cost Pumping Sludge Main $330,000 Sludge Thickening $570,000 Digestion - Mesophilic $500,000 FSBs $130,000 Dredging $120,000 DLD $240,000 Projected Annual O&M Costs $1,890,000

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Chapter 12. Capital Improvement Plan/Financial Plan

Objective The recommended improvements to the existing system at the SHDF are intended to be implemented in stages over the planning period (2003-2025). Some of the recommended improvements to the SHDF, described herein, are contingent upon actual population growth and loading, others are new processes or process modifications, and some are dependent on pilot test results. Therefore, the actual scope and need for some of the improvements can only be estimated at this time since the timing of the improvements will be determined by future conditions or test results.

Capital Improvements Plan Figure 12-1 depicts the proposed implementation schedule for the recommended improvements. The schedule includes the time required for total project implementation, beginning with pilot testing if necessary), to preliminary design, and concluding with start-up. Shown on the schedule are projected loadings in 5-year increments beginning in 2005 through 2025 for raw sludge loading, FSB loading, and DLD area loading.

Table 12-1 displays the expected cost disbursement plan for the preferred system. This table represents an estimate of when expenditures would be necessary to implement the recommended improvements on the schedule shown on Figure 12-1. Figure 12-2 displays the program capital expenditures. All costs are stated in year 2003 dollars.

Detailed Project Information Sheets The following pages contain information on each recommended improvement or project.

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Component Estimated Year Cost 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025

Projected Average Raw Sludge Loading -- (City-Based), dry tons per day 45.70 49.00 52.40 55.80 59.10

Projected Average FSB Loading (Digester -- Discharge) (City-Based), dry tons per day 25.60 27.40 29.30 31.20 33.10 Projected DLD Loading (City-Based), -- tons per year 7,000 7,500 8,000 8,500 9,000 Pilot Test: Iron Chloride at BSPS for Struvite Control $200,000 Grease Handling Improvements $350,000 Sludge Thickening Pilot Tests (Centrifuge and GBT) $250,000 Sludge Thickening 1 $8,600,000 Centrate Treatment 2 $2,690,000 Study to evaluate aquifer production capability $80,000 Irrigation System 2 $1,420,000 Structural Integrity Review of Digesters 1 to 4 $20,000 Digester Improvements (Units 1 to 4) 3 $7,210,000 FSB Expansion $3,630,000 FSB Dredge Rehabilitation $130,000 DLD Tillage Testing 4 $100,000 DLD Injection Equipment 4 $230,000 Recommended Improvements $24,910,000 1 Should the RFBB be installed in 2008, potential conversion of thickening centrifuges to dewatering or partial dewatering centrifuges would occur in 2007-2008. A cost for this conversion is not included. 2 Should the LFWRF be constructed at the Clear Spring Ranch site, centrate treatment and irrigation may not be necessary, depending on timing of plant construction. The LFWRF should be designed to accept/treat the centrate flows if constructed at Clear Spring Ranch. 3 Timing based on results of Structural Integrity Review. 4 A DLD tillage study is recommended in 2004 to determine tillage potential and proper equipment selection. If tillage is successful, DLD tillage equipment purchase is recommended in 2005- 2006. Costs for the tillage equipment not included. One TerraGator is recommended during the planning period for future increased loading (cost included-2015). Figure 12-1. Proposed Implementation Schedule

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Year Component Estimated Cost 5 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017-2025 Pilot Test: Iron Chloride at BSPS for Struvite Control $200,000 $200,000 Grease Handling Improvements $350,000 $50,000 $300,000 Sludge Thickening Pilot Tests (Centrifuge and GBT) $250,000 $250,000 Sludge Thickening 1 $8,600,000 $860,000 $2,580,000 $5,160,000 Centrate Treatment 2 $2,690,000 $270,000 $2,420,000 Study to evaluate aquifer production capability $80,000 $80,000 Irrigation System 2 $1,420,000 $140,000 $1,280,000 Digester Structural Integrity Review (Units 1 to 4) $20,000 $20,000

Digester Improvements (Units 1 to 4) 3 $7,210,000 $730,000 $3,240,000 $3,240,000 FSB Expansion $3,630,000 $360,000 $3,270,000 FSB Dredge Rehabilitation $130,000 $130,000 DLD Tillage Testing 4 $100,000 $100,000 DLD Injection Equipment 4 $230,000 $230,000 Totals $24,910,000 $650,000 $1,320,000 $6,580,000 $5,160,000 $0 $360,000 $3,270,000 $0 $130,000 $0 $730,000 $3,470,000 $3,240,000 $0

1 Should the RFBB be installed in 2008, potential conversion of thickening centrifuges to dewatering or partial dewatering centrifuges would occur in 2007-2008. A cost for this conversion is not included. 2 Should the LFWRF be constructed at the Clear Spring Ranch site, centrate treatment and irrigation may not be necessary, depending on timing of plant construction. The LFWRF should be designed to accept/treat the centrate flows if constructed at Clear Spring Ranch. 3 Timing based on results of Structural Integrity Review. 4 A DLD tillage study is recommended in 2004 to determine tillage potential and proper equipment selection. If tillage is successful, DLD tillage equipment purchase is recommended in 2005-2006. Costs for the tillage equipment not included. One TerraGator is recommended during the planning period for future increased loading (cost included-2015). Table 12-1. Expected Cost Disbursement

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$7,000,000 2005 and 2006: Includes Design and Construction for Thickening System (partial), Centrate Treatment, Includes Digester Water Management System, and Grease Handling Improvements Improvements (Units 1 to 4 (year $6,000,000 2)) Includes Pilot Testing and/or Studies for Includes Construction of Chemical Addition at Thickening System (year 2) Includes Additional BSPS, Sludge $5,000,000 TerraGator for DLD Thickening, Aquifer Includes Design and System Production Capability, Construction of Digester Digester Structural Includes Design and Improvements (Units 1 to Integrity Review, and Construction of 2 4) (Timing Dependent on $4,000,000 DLD Tillage Field Trials Additional FSBs Structural Integrity Review)

$3,000,000 Annual Projected Expenditure

$2,000,000

Includes Rehab of FSB Dredge

$1,000,000

$0 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Year Figure 12-2. Program Capital Expenditures

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Project Type: Iron Chloride Testing at BSPS

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: 2004

Preliminary Cost Estimate: $200,000 (2003 dollars)

Project Need: The large amount of material discovered in Digester 7 in 2003 was determined (through testing) to be almost entirely struvite scale. Colorado Springs Utilities plans to take an older digester offline next year and clean it out to determine its struvite situation.

Iron chloride is often used to precipitate phosphate from solution and thus minimize the production of struvite within digesters. However, iron will react with both sulfide and phosphate, and has some preference for sulfide. Therefore, to have an impact in reducing the phosphate concentration in the digesters, more sulfide will probably be precipitated as well. Thus, the iron chloride dose could rise significantly to achieve major phosphate reduction within the digesters.

Adding iron chloride directly at the SHDF digestion complex is possible, however, iron should not be added anywhere near where the sludge is being heated. Therefore, iron should not be added to the raw sludge being transported through a heat exchanger. Iron chloride can be added directly to each digester; however, this requires multiple feedpoints typically through the sidewall of the digesters.

Iron chloride can also be added at the BSPS wetwell at the Las Vegas Street WWTP. This would be a relatively easy chemical addition point and would be helpful in keeping sulfide levels controlled within the Sludge Main.

Project Description: A pilot test is recommended by which iron chloride is added at the Las Vegas Street WWTF BSPS to test phosphate control in digester feed sludge, and thereby greatly minimize struvite production. Colorado Springs Utilities staff are continuing the phosphate and related testing of sludge and should have results to help confirm if phosphate solubilization during Sludge Main travel is the likely cause of the extraordinary struvite scale deposits in the digesters. After pilot testing iron chloride addition at BSPS, and with the latest data available, Colorado Springs Utilities should revisit the struvite problem and solutions.

Possible Equipment: Either a mobile or fixed iron chloride feed system at the BSPS can be used over a several month testing period.

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Project Drivers:

§ To determine if struvite in the digesters can be controlled through a reasonable iron chloride chemical feed system. § If iron chloride (at reasonable cost) can work, it might delay or minimize the need for the thickening facilities at the SHDF.

Project Impacts: If the iron chloride test is not completed, Colorado Springs Utilities staff will not have the benefit of this possible solution to the struvite problem at the SHDF digesters.

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Project Type: Grease Handling Improvements

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: 2005 and 2006

Preliminary Cost Estimate: $350,000 (2003 dollars)

Project Need: In order to alleviate the surges in gas production and foul air in the grease handling building, changes in operations of the existing grease handling system are required.

Project Description: The recommended improvements include:

§ Keeping the grease warm in the truck while it is being filled at the Las Vegas Street WWTF. § Beginning injection immediately into the digesters when the truck arrives at the SHDF. § Improving HVAC in the grease handling building to better protect operator health.

Possible Equipment: § Tanker truck § Truck heating system (at the Las Vegas Street WWTF) § HVAC improvements to the grease building

Project Impacts: The following existing problems could become worse as plant loading increases:

§ The tanker truck with congealed grease will not be able to empty in time to return to the Las Vegas Street WWTF and accept grease from the concentrator. § Someone could become ill by breathing the air in the grease building. § Gas handling equipment could be damaged or overloaded by surges that accompany grease injection.

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Project Type: Raw Sludge Thickening

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: 2004: Pilot Testing 2005: Design 2006 & 2007: Construction

Preliminary Cost Estimate: Pilot Testing: $250,000 (2003 dollars) Raw Sludge Thickening: $8,600,000 (2003 dollars)

Project Need: With about two-thirds of the new 14-inch diameter Sludge Main installed, the average transit time has increased dramatically, and the velocity is less than 0.5 ft/second. Based on sludge characteristics at the pipe discharge, acid phase digestion is occurring within the pipe, with discharge volatile fatty acids (VFAs) of about 3,000 mg/L, low pH (average about 6.0), and some solubilization of volatile solids in transit. There was reported to be relatively limited gas production in the Sludge Main prior to the first 14-inch sections coming on-line in 1999/2000.

The very low velocity and high transit times now occurring in the Sludge Main are causing more gas production in the pipeline and may be causing the production of struvite in the digesters. A velocity range of about 1.0 ft/sec in the Sludge Main is recommended to reduce transit times to acceptable levels. As velocity rises, flowrate rises, and sludge with reduced solids content must be pumped. As a result of pumping sludge to the SHDF with a lower solids content, it will be necessary to thicken the raw sludge before introducing it to the digesters.

Project Description: Thickening centrifuges are the recommended process to handle the proposed increase in water arriving at the SHDF. The centrate will be partially fermented, with a low pH, and odorous, therefore the thickening process must be fully contained to avoid odor problems.

Pilot testing is recommended for the proposed sludge thickening process. Both centrifuges and GBTs should be pilot tested.

The thickening system will be contained in a new structure (concrete building approximately 90 feet x 80 feet) near the current Sludge Main discharge point and adjacent to the digesters. From the Sludge Main discharge, the flow will be diverted and flow to new raw sludge storage tanks with mixing capability and then pumped to new thickening centrifuges. After thickening, the sludge will be pumped either to new thickened sludge storage tanks or directly to the existing wetwell, with added mixing. The thickened sludge will then be pumped to the existing digesters. The thickening system will consist of mixed raw sludge storage tanks, three thickening centrifuges with feed pumps, a polymer system, power supply, control systems, odor control, thickened sludge storage/mix tanks, and thickened sludge pumping facilities.

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Possible Equipment: Decanter-type centrifuges are recommended for this application because of odor considerations and the ability of the centrifuges to operate unattended or with minimal attention in a 24 hr/day, 7 day/week operating mode. Although centrifuges are recommended, Colorado Springs Utilities may wish to further evaluate the use of gravity belt thickeners.

Project Drivers: Adding thickening prior to the digestion process is recommended for several reasons:

§ To allow reduced sludge residence time in the Sludge Main by pumping thinner sludge, and thereby reduce struvite production. § Reduce the number of digesters that need to be operated in the near-term and long- term. § Cut sludge heating requirements as a result of reduced digester feedrates.

In addition, thickening centrifuges can be converted to function as dewatering centrifuges. This potential conversion should be investigated further and discussed during the pilot testing. This would allow dewatering capability should a RFBB be installed in the future at the Ray Nixon Power Plant. A cost for this potential conversion is not included in the capital cost estimate.

Project Impacts: Impacts of not completing the proposed project include the following.

§ Continued acid-phase digestion occurring in the Sludge Main, which produces a chemical environment favorable to the formation of struvite, gas production in the pipeline, and a very odorous mixture in the sludge wetwell. § Increase in the number of digesters that need to be operated in the near-term and long-term.

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Project Type: Centrate Treatment (Generated from Raw Sludge Thickening)

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: 2005: Design 2006: Construction

Preliminary Cost Estimate: $2,690,000 (2003 dollars)

Project Need: Centrate treatment is required to treat the water created by sludge thickening. The centrate characteristics will make it difficult to handle primarily because of the solubilization and acidification that has occurred within the Sludge Main. Discharging the centrate to the open Supernatant Lagoons would be ill-advised due to odor emissions and potential groundwater infiltration. Discharging the centrate directly to the FSBs will also be unacceptable for both odor emission reasons as well as potentially upsetting the biology within the FSBs. The quantity of centrate flow totals between 400 and 600 acre-feet per year assuming a Sludge Main flow of about 0.70 mgd.

Project Description/Equipment: An upflow anaerobic sludge blanket reactor is recommended at this time for centrate treatment. The centrate would be pumped through a packaged, skid mounted system. The process would consistently remove high levels of COD and nitrogen compounds before the treated centrate flows to the FSBs for polishing.

Project Considerations: The LFWRF is a proposed wastewater treatment facility currently being planned for the southern Colorado Springs Metropolitan Area to treat flows from the Jimmy Camp Creek Basin. Preliminary results of the ongoing Siting Study indicated that the Clear Spring Ranch site is the most favorable location for the LFWRF. Should this new WRF be constructed at the Ranch, separate centrate treatment would not be necessary to treat the centrate produced from the thickening centrifuges, however the LFWRF would need to be designed to accept and treat the centrate flows.

Project Impacts: Impacts of not completing the proposed project include the following:

§ Odor concerns. § Potential groundwater infiltration.

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Project Type: Water Management System

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: 2005: Aquifer Study 2005: Irrigation System Design 2006: Construction

Preliminary Cost Estimate: Study: $80,000 (2003 dollars) Irrigation System: $1,420,000 (2003 dollars)

Project Need: A study is planned to provide a means to handle excess water in the event the groundwater levels rise to the point that action is needed.

In addition, the centrate generated during thickening will need to be prevented from building up in the groundwater. The water generated from thickening must be treated before the water can be used elsewhere. After treatment, the centrate or filtrate will be conveyed to the FSBs, where additional biological treatment occurs naturally. The water from these operations eventually flows to the Supernatant Lagoons. Excess water from these lagoons could be handled by an on-site irrigation system.

Project Description: The study should contain aquifer testing in selected areas to determine if water can be removed from local areas to prevent problems relating to rising groundwater. The testing will consist of well pumping and geological testing as required for a hydrogeological evaluation.

At this time and for purposes of cost planning, we assume that an irrigation system at Clear Spring Ranch will be implemented. The irrigation system will consist of a pump station at the Supernatant Lagoons, a pipeline to route the flow to the proposed irrigated area immediately west of I-25, and spray irrigation equipment. A study is needed initially to determine the types of crops that can be grown with this water considering the climate and soil conditions. Alternative sites at the SHDF should be evaluated to find the best arrangement a at reasonable cost.

Project Drivers: § Need to handle excess water at the SHDF to prevent groundwater buildup. § On-site irrigation appears to be the least costly approach at this time.

Project Impacts: If required, removal of excess water from the shallow aquifer will be needed to prevent boggy areas in the DLDs, to make sure contaminated groundwater does not escape from the closed basin, and to limit hydraulic pressure on the dam.

If excess water is not handled properly at the SHDF, groundwater contamination is very likely with off-site impacts eventually causing severe adverse regulatory activity for Colorado Springs Utilities.

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Project Type: FSB Expansion

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: 2009: Design 2010: Construction of FSBs 2012: Dredge Rehabilitation

Preliminary Cost Estimate: FSB Expansion: $3,630,000 (2003 dollars) FSB Dredge Rehabilitation: $130,000

Project Need: In order to remain under the design FSB loading rate of 20 lbs. VS / 1,000 ft2 / day (average annual), two additional FSBs are recommended in 2010 to meet future loading projections.

Project Description: Currently, there are nine FSBs at the SHDF. Three new FSBs were constructed as part of the 1998 expansion. The FSBs are 15-foot liquid depth basins with a surface area of 5 acres each (45 liquid surface acres total).

It is anticipated that regulators may require impermeable lining for new FSBs (i.e., groundwater protection). The proposed location of the two new units is north of the existing FBSs.

The existing FSB dredge was purchased in 1999. It is assumed that the existing dredge will need to be rehabilitated at some point during the planning period (estimated in 2012).

Project Drivers: Additional FSBs are required to meet future capacity needs based on the annual average design loading rate of 20 pounds VS/1,000 sq ft/day.

Project Considerations: A major issue at the SHDF would be whether the FSB loading rate could be increased. The 20 pounds VS/1,000 sq ft/day loading rate (annual avg.), is based on extensive work at the Sacramento Regional WWTP in full-scale testing in the late 1970s, as well as full-scale monitoring over the years at this plant.

Therefore, perhaps at the SHDF, with its more remote location, increased loading of FSBs could be tolerated. This is something that would need to be tested over time to determine what loading rate can be accommodated, but there is a reasonable chance that the loading rate could be increased to 25 lb VS/1,000 sq ft/day, therefore gaining more capacity from existing units and possibly delaying the need for construction of new FSBs. When the loading rate becomes too high, the aerobic water cap layer will start to lose its odor treatment capability, and stronger odors will break through the basin cap layer and be emitted to the atmosphere. So, preserving the aerobic cap layer is the crucial element for FSB odor control. The brush aerators are important in this function in that they insure little debris or scum is on the surface which would inhibit natural aeration of the surface water through wind action.

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If higher loading rates are used, then the FSBs will fill up somewhat faster with solids, and would need to be dredged more often. Currently, the FSBs are on approximately a 3 to 5 year dredging schedule (i.e., dredge two FSBs every year.) For instance, if a 25 percent higher feedrate is used (25 lbs versus 20 lbs), then Colorado Springs Utilities may need to change to a 3-year dredging schedule. This is not expected to be a problem, but a somewhat more frequent dredging schedule may reduce slightly the VSR achieved within the FSBs. Currently, data indicates that about 34 percent VSR is achieved within the FSBs, over the course of the 2 to 3 year average storage time within the FSBs. Most of the VSR is achieved in the first year, with reduced destruction each year thereafter.

Project Impacts: The existing FSB capacity will be exceeded in 2010, based on projected loadings. The danger in exceeding loading rates is primarily downwind odor from the FSBs.

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Project Type: Digester Improvements (Units 1 Through 4)

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: 2004: Structural Integrity Review 2014: Design (Actual timing depends on results of Structural Integrity Review) 2015 & 2016: Construction

Preliminary Cost Estimate: Structural Integrity Review: $20,000 (2003 dollars) Digester Improvements: $7,210,000 (2003 dollars)

Project Need: At some time in the future (estimated in 2016 for planning purposes – actual timing depends on equipment condition), conversion of digester covers (units 1 through 4) to submerged- fixed type and to a mechanical draft tube mixing system is recommended. A structural integrity review of the digesters should occur to determine the need for the cover replacement, mixing, and structural improvements. This modification is recommended to prevent the floating covers from causing problems as they age, for foam control, to have automated mixing control, and achieve increased capacity and reliability. Although recommended for planning purposes, Colorado Springs Utilities may wish to further evaluate improvements as additional experience is gained.

Project Description: The existing floating covers, gas recovery, and mixing equipment on Digesters 1 through 4 will be replaced with submerged fixed covers and mechanical drat tube mixers like those on Digesters 5 through 8.

Project Drivers: Submerged-fixed digester covers are recommended for replacement for the existing original four digesters because it provides the following:

§ Increased usable volume by 25 percent over existing floating cover tanks. This equates to a 25 percent increase in digester detention time as well. § Lower maintenance requirement by eliminating foaming on the digester roof and condensation build-up in the digester cover. § Fugitive digester gas emissions can be eliminated because there is no annular space between the digester cover and the tank walls. § In the future, the gas pressure can be increased to improve the boiler operation. § Provides consistency with 4 newer units (Digesters 5 through 8).

Project Impacts: Without the project, Colorado Springs Utilities will not gain the benefits of increased capacity and other drivers identified. If structural concerns are identified within the study phase, there could be further consequences.

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Project Type: DLD Tillage and Equipment

Project Identified: December 2003, Clear Spring Ranch SHDF Masterplan

Estimated Schedule: DLD Tillage Testing (Field Trials): 2004 Tillage Equipment: 2005-2006 (if purchased) DLD Injection Equipment: 2015

Preliminary Cost Estimate: DLD Tillage Testing (Field Trials): $100,000 (2003 dollars) DLD Injection Equipment (TerraGator): $230,000 (2003 dollars) Costs for DLD Tillage Equipment is not included.

Project Need: One TerraGator should be added during the planning period for future loadings.

Project Drivers: It is assumed that tillage will increase evaporation and the application rate so that no additional DLD acreage would be needed. Testing should be performed to determine an appropriate tillage schedule and determine target increased evaporation rates. Disks and plows may not be compatible with rocky areas; some type of shallow subsoiler may work better. Reduced DLD acreage and a more efficient system is possible if increased evaporation can be achieved.

Project Considerations: Colorado Springs Utilities should perform field trials before equipment selection and purchase. It is recommended to rent different equipment types and determine which works best, and then decide what to purchase. Therefore, tillage equipment costs are not included in the capital costs.

DLD operation is clearly limited at times due to wet soils and trafficability for application vehicles. The climate at Clear Spring Ranch should be considered to determine evaporation potential. The goal of this operating strategy is to promote evaporation rather than infiltration.

The best way to define capacity is to isolate one representative DLD unit (or portion of a DLD area) and conduct a more systematic operation. This would include running the TerraGator at constant speed and known discharge rate to achieve a certain application.

An agricultural wheel tractor (approx. 100 hp) should be rented along with a heavy plow and construction disk. If purchased, equipment could be pre-owned to minimize investment until it is clear what works best. For example, rocks that are common in DLD soils will interfere with operation of some tillage implements.

Operational experience will then define limits for DLD operation. If one inch/week of liquid application is satisfactory, additional loading should be tested. Maintain a record of applications with comments regarding success or problems. Results will allow refinement of site capacity projections.

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Project Impacts: Based on projected loadings in 2025, expanding the current 194-acre DLD operation area by a total of 100 acres would be necessary if higher DLD loading rates are not possible. A 36-acre expansion is expected to be complete in 2004, therefore an additional 64 acres will be necessary. Estimated cost for the DLD expansion is $2,500 per acre. Tillage could result in significant cost savings.

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Chapter 13. References

Black and Veatch, 1997. Hanna Ranch Master Plan.

Brown and Caldwell, April 1980. Long-Range Sludge Management System Facility Plan.

Brown and Caldwell, May 8, 1997. Hanna Ranch SHDF Expansion Basis of Design Memorandum.

Brown and Caldwell, 2000. Lined Dedicated Land Disposal Project - Design Confirmation Report. Prepared for the Sacramento Regional County Sanitation District, August 2000.

Brown and Caldwell, 2003. Draft Report - "Producing Class A Biosoilds with Low-Cost, Low- Technology Treatment Processes" Report for Water Environment Research Foundation, Alexandria, Virginia.

CH2M/Hill, 1998. Supernatant Management Plan and Zero Discharge Treatment Evaluation – Hanna Ranch Facility.

Colorado Air Pollution Control Division (APCD), July 31, 2003. Air Quality Compliance Inspection Colorado Springs Utilities – Hanna Ranch Solids Handling & Disposal Facility

Colorado Department of Public Health and Environment, February 1, 2001. Operating Permit -- Number 96OPER152.

Colorado Springs Utilities, January 15, 2002. Preliminary Report Clear Spring Ranch Excess Water Study.

Metcalf & Eddy, 1991. Wastewater Engineering, Treatment, Disposal, and Reuse.

Montgomery Watson, December 31, 2000. Colorado Springs Utilities Wastewater Infrastructure Strategic Plan.

MWH, August 18, 2003. Memorandum RE: Lower Fountain Regional Water Reclamation Facility Siting Study.

Schafer, P., J. Farrell, G. Newman, S. Vandenburgh, October 2002. Advanced Anaerobic Digestion Performance Comparisons. Presented at WEFTEC Conference, Chicago, Illinois.

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\FINAL REPORT\Chapter 13.doc 13-1 Appendix A Cost/Economic Criteria and Assumptions for the Solids Evaluation of the Clear Spring Ranch SHDF Masterplan

Appendix A Cost/Economic Criteria and Assumptions for the Solids Evaluation of the Clear Spring Ranch SHDF Masterplan

This appendix provides cost criteria and assumptions and the basis for the economic analysis for comparison of solids processing alternatives for the Clear Spring Ranch SHDF Masterplan.

Capital Cost Assumptions Construction cost estimates for facilities are based on costs for year 2003.

In some cases, yard piping is separately estimated. In other cases, yard piping is included in the costs for larger facilities.

A 30% construction contingency is included to account for facilities elements and details not identified at this planning-level stage.

An allowance of 25% is included to account for engineering design, program management, administration, engineering services during construction, and related costs. Refined costs for the recommended alternative included an allowance of 18%.

For the economic analysis of solids alternatives, Net Present Value (NPV) analysis has been done over a twenty year span, using both capital and operating costs. An interest rate of 5% has been used in the analysis. The alternatives were compared for two cases, assuming projected growth of the City, and assuming that the facility treats all of the sludge in the County, projected to the year 2025.

O&M Cost Assumptions Labor is based on $60,000 per year per person (average). This is a fully loaded cost (i.e., with fringes and overhead).

Maintenance is based on 2 percent per year of the installed cost of net new equipment.

Chemicals costs are assumed to be at current prices – i.e., lime at $62/ton, dewatering polymer at $0.78 per pound, and thickening polymer at $1.28 per pound.

Natural gas/Diesel fuel cost is based on $8 per million BTUs.

No inflation rate is assumed for the Operation and Maintenance costs.

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\FINAL REPORT\Appendix A.doc A-1 Appendix B Explanation of Comparison Ratings in Table 7-1

Appendix B Explanation of Comparison Ratings in Table 7-1

This appendix provides brief explanations of the comparison criteria used for the ratings shown in Table 7-1 of Chapter 7.

Flexibility Flexibility is a measure of how differently the products can be ultimately managed. This factor is also a measure of how the sludge processing system can perform under varying sludge input conditions, staffing level changes, and potential chemicals supply disruption. Simpler digestion processes tend to rate high in this category, and the more complex systems that produce a less flexible product rate lower.

Ease of O&M This category is judged by the degree of staffing required and the level of complexity of the systems that must be operated and maintained. Aerobic digestion rates high in this category, as well as most anaerobic digestion systems. However, more complex drying and incineration systems rate lower, as well as lime slaking.

Proven System This category rates whether and how well the alternative has operated at the required scale in sufficient applications in North America.

Reliability Reliability is a measure of the dependability and ruggedness of the technology and the system, the probability for upset or failure, likely downtime for maintenance, and similar factors. The more complex processing systems generally rate lower in this category.

Ability to Construct This factor rates the constructability of the alternative, the availability of construction contractors and contractor experience, and specialized equipment and resources required. Systems that have been implemented only a few times rate lower in this category than systems that have been implemented many times at the required scale.

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Odor Potential This category rates alternatives on their ability to avoid off-site odors. A high degree of odor control is provided for each alternative as described in Chapter 7, so this factor evaluates the ability of these odor control systems to work reliably and operate continuously at a high performance level with limited staff involvement and attention. This factor also includes the likely odor impacts of the final product during transportation and at final use/disposal sites.

Product Use/Recycle This factor rates the beneficial use potential of the final products produced – i.e., biosolids products and digester gas. Products that have maximum desirability from the ultimate user standpoint are rated highest.

Water Impact This factor rates the alternatives on impact to water quality - both internal plant water quality from solids recycle streams (i.e., ammonia from digestion), and off-site water quality impacts from use/disposal of the final products.

Air Impact This factor rates the alternatives on impact to air quality, other than odor impacts. This includes combustion emissions, volatile organic compounds, and greenhouse gases. Quantitative emission calculations are not made to support these ratings, but rather results from previous projects are used as a general guide. Trucking emissions are included in the rating.

Acceptability This factor rates perceived public acceptability of the alternative. One rating is for the local community and the other rating is for the area beyond the local community – i.e., taking into account the broader public in the region.

Regulatory/Permits This factor rates the expected ease in obtaining permits and regulatory approvals and the community perception of complying with the required rules and regulations.

End Use Control This factor relates to the degree of control– especially in the area of overall biosolids management and the final disposition of the products.

Trucking This factor relates to the quantity of final sludge/biosolids products trucked off-site and the degree of offensiveness of this material. The greater the trucked quantities, the lower the rating.

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\FINAL REPORT\Appendix B.doc B-2 Appendix C Detailed Cost Estimates

PROJECT NAME: Clear Spring Ranch SHDF Master Plan PROJECT NO: 23559 DATE: 22-Dec-03 PREPARED BY: DAM FACILITY DESCRIPT: Alt 1 - Grease Handling Improvements SHEET NAME: Preliminary Cost Estimate

Construction Total Construction Engineering, legal Description Unit Quant. Unit Cost Installed Equipment Cost contingency costs Costs and admin costs Total costs Source ************************************************** ****************** ***************** ********************* ************************************************************************************************************************* ********************************************************

Tanker truck ea 1 $100,000 $100,000 $30,000 $130,000 $23,000 $153,000 Unknown Heating system at LVSWRF ls 1 $50,000.0 $50,000 $15,000 $65,000 $12,000 $77,000 Internal estimate + vendor quotes HVAC improvements grease bldg. ls 1 $75,000 $75,000 $23,000 $98,000 $18,000 $116,000 Internal estimate + vendor quotes ************************************************** ****************** ***************** ********************* ********************* *********************** *************************** *********************** *********************** ******************************************************** SUBTOTALS $225,000 $68,000 $293,000 $53,000 $346,000

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\DRAFT Report\Appendix C.xls\Grease Handling Impr. PROJECT NAME: Clear Spring Ranch SHDF Master Plan PROJECT NO: 23559 DATE: 22-Dec-03 PREPARED BY: DAM FACILITY DESCRIPT: Alternative 1 - Thickening SHEET NAME: Preliminary Cost Estimate

Construction Total Construction Engineering, legal Description Unit Quant. Unit Cost Installed Equipment Cost contingency costs Costs and admin costs Total costs Source ************************************************ ***************** **************** ********************* *************************************************************************************************************************** ******************************************************

1 Pipeline diversion/bypass structure ea 1 $250,000 $250,000 $75,000 $325,000 $59,000 $384,000 Means Raw sludge storage tank - 2@ 75,000 2A gallons gal 150,000 $2.5 $375,000 $113,000 $488,000 $88,000 $576,000 Derived from previous projects Sludge storage tank bottom - 32' dia x 2B 8" thick cast concrete (2 tanks) cu yd 50 $300 $15,000 $5,000 $20,000 $4,000 $24,000 Means plus Contractor input Centrifuge feed pumps - Centrifugals, 3 500 gpm each, 3 pumps ea 3 $17,000 $51,000 $15,000 $66,000 $12,000 $78,000 Derived from previous projects 4 Centrifuges - ALDEC 706G2 ea 3 $600,000 $1,800,000 $540,000 $2,340,000 $421,000 $2,761,000 Vendor quote 5A Polymer addition tank ea 1 $15,000 $15,000 $5,000 $20,000 $4,000 $24,000 Vendor quote 5B Polymer pump ea 2 $3,000 $6,000 $2,000 $8,000 $1,000 $9,000 Derived from previous projects 5C Polymer Pump--Controls ea 1 $2,000 $2,000 $1,000 $3,000 $1,000 $4,000 Discussion with BC electrical engineer 5D Polymer Pump--Miscellaneous ea 1 $5,000 $5,000 $2,000 $7,000 $1,000 $8,000 Derived from previous projects Thickened sludge storage - 2 tanks 10,000 gal each, hopper bottom with 6 steel legs gal 20,000 $5 $100,000 $30,000 $130,000 $23,000 $153,000 Based on vendor quote for another project 7 improvements ea 1 $100,000 $100,000 $30,000 $130,000 $23,000 $153,000 Retrofit wet well, estimated from other projects Thickened sludge feed pumps - 8 centrifugals, 120 gpm each, 3 pumps ea 3 $10,000 $30,000 $9,000 $39,000 $7,000 $46,000 Derived from previous projects 9A Building - cast in place floors yd 250 $250 $62,500 $19,000 $82,000 $15,000 $97,000 Means 9B Building - cast in place walls yd 400 $400 $160,000 $48,000 $208,000 $37,000 $245,000 Means 9C Building - pads curbs, etc. yd 10 $200 $2,000 $1,000 $3,000 $1,000 $4,000 Means 9D Building - twin T roof sf 7,500 $13 $97,500 $29,000 $127,000 $23,000 $150,000 Means 9E Building - electrical and mechanical sf 7,500 $17 $127,500 $38,000 $166,000 $30,000 $196,000 Means plus experience 9F Building - architectural finish sf 7,500 $20 $150,000 $45,000 $195,000 $35,000 $230,000 Means plus experience Building - structural excavation and 9G backfill yd 5,000 $10 $50,000 $15,000 $65,000 $12,000 $77,000 Means Process piping - 2,000', 8" average, on 10 hangers ft 2,000 $60 $120,000 $36,000 $156,000 $28,000 $184,000 Estimated from other projects plus Means Yard piping - 3,000', 8" average, buried 11 5' deep ft 3,000 $80 $240,000 $72,000 $312,000 $56,000 $368,000 Estimated from other projects plus Means 12 Thickening Odor control cfm 14000 $45 $630,000 $189,000 $819,000 $147,000 $966,000 BC Odor expert 13 Plant electrical service ea 1 $900,000 $900,000 $270,000 $1,170,000 $211,000 $1,381,000 Approx 15% 14 Sitework yd 10000 $6 $60,000 $18,000 $78,000 $14,000 $92,000 Means Bridge crane for equipment 15 maintenance ea 1 $200,000 $200,000 $60,000 $260,000 $47,000 $307,000 Based on vendor quote for another project Miscellaneous steel - stairs, ladders, 16 platforms ton 15 $3,000 $45,000 $14,000 $59,000 $11,000 $70,000 Means ************************************************ ***************** **************** ********************* ************************ ********************** *************************** ********************** ************************* ****************************************************** SUBTOTALS $5,593,500 $1,681,000 $7,276,000 $1,311,000 $8,587,000

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\DRAFT Report\Appendix C.xls\Thickening PROJECT NAME: Clear Spring Ranch SHDF Master Plan PROJECT NO: 23559 DATE: 22-Dec-03 PREPARED BY: DAM FACILITY DESCRIPT: Alternative 1 - Centrate Treatment SHEET NAME: Preliminary Cost Estimate

Construction Total Construction Engineering, legal Description Unit Quant. Unit Cost Installed Equipment Cost contingency costs Costs and admin costs Total costs Source ************************************************** ****************** ***************** ********************* ************************************************************************************************************************* ********************************************************

Centrate Treatment - packaged system, 1 upflow anaerobic sludge blanket reactor ea 2 $750,000 $1,500,000 $450,000 $1,950,000 $351,000 $2,301,000 Vendor quote Ancillary equipment - concrete pad, 2 piping connections, utilities, installation ea 1 $250,000 $250,000 $75,000 $325,000 $59,000 $384,000 Vendor's estimate ************************************************** ****************** ***************** ********************* ********************* *********************** *************************** *********************** *********************** ******************************************************** SUBTOTALS $1,750,000 $525,000 $2,275,000 $410,000 $2,685,000

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\DRAFT Report\Appendix C.xls\Centrate Treatment PROJECT NAME: Clear Spring Ranch SHDF Master Plan PROJECT NO: 23559 DATE: 22-Dec-03 PREPARED BY: DAM FACILITY DESCRIPT: Alternative 1 - Irrigation System SHEET NAME: Preliminary Cost Estimate

Construction Total Construction Engineering, legal Description Unit Quant. Unit Cost Installed Equipment Cost contingency costs Costs and admin costs Total costs Source ************************************************** ****************** ***************** ********************* ************************************************************************************************************************* ********************************************************

Irrigation pumphouse - 3 pumps @ 500 gpm, bleach injection, floating pond 1 intake ea 1 $250,000 $250,000 $75,000 $325,000 $59,000 $384,000 Derived from previous projects 2 Irrigation piping - 2 miles of 8" DI pipe ft 10,560 $50 $528,000 $158,000 $686,000 $123,000 $809,000 Means 3 Spray equipment ea 1 $150,000 $150,000 $45,000 $195,000 $35,000 $230,000 Estimated from catalog pricing ************************************************** ****************** ***************** ********************* ********************* *********************** *************************** *********************** *********************** ******************************************************** SUBTOTALS $928,000 $278,000 $1,206,000 $217,000 $1,423,000

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\DRAFT Report\Appendix C.xls\Irrigation System PROJECT NAME: Clear Spring Ranch SHDF Master Plan PROJECT NO: 23559 DATE: 22-Dec-03 PREPARED BY: DAM FACILITY DESCRIPT: Alternative 1 - FSB construction SHEET NAME: Preliminary Cost Estimate

Construction Engineering, legal and Description Unit Quant. Unit Cost Installed Equipment Cost contingency costs Total Construction Costs admin costs Cost per FSB Total Cost (2 FSBs) Source ****************************************** ******************* ***************** ********************** ************************ ***************************************************************************************************************************************************************************************************************

COST PER 5 ACRE LAGOON 1 Excavation yd 60,000 $3 $180,000 $54,000 $234,000 $42,000 $276,000 $552,000 Means 2 Lining sq ft 270,000 $2.5 $675,000 $203,000 $878,000 $158,000 $1,036,000 $2,072,000 Vendor Quote 3 8" gravel layer on liner bottom yd 5,400 $10 $54,000 $16,000 $70,000 $13,000 $83,000 $166,000 Means 4 Concrete ramp yd 16 $250 $4,000 $1,000 $5,000 $1,000 $6,000 $12,000 Means 5 Concrete structures yd 20 $400 $8,000 $2,000 $10,000 $2,000 $12,000 $24,000 Means 6 Mechanical equipment ls 1 $100,000 $100,000 $30,000 $130,000 $23,000 $153,000 $306,000 Based on recent construction 7 Piping ft 1,500 $75 $112,500 $34,000 $146,500 $26,000 $172,500 $345,000 Means 8 Electrical ls 1 $50,000 $50,000 $15,000 $65,000 $12,000 $77,000 $154,000 Based on recent construction ****************************************** ******************* ***************** ********************** ************************ *************************************************************************************************************************************************************************************************************** SUBTOTALS $1,183,500 $355,000 $1,538,500 $277,000 $1,815,500 $3,631,000

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\DRAFT Report\Appendix C.xls\FSB Expansion PROJECT NAME: Clear Spring Ranch SHDF Master Plan PROJECT NO: 23559 DATE: 22-Dec-03 PREPARED BY: DAM FACILITY DESCRIPT: Alternative 1 - Digester Modifications SHEET NAME: Preliminary Cost Estimate

Construction Total Construction Engineering, legal and Total Cost (4 Digester Description Unit Quant. Unit Cost Installed Equipment Cost contingency costs Costs admin costs Cost per Digester Mod. Mods) Source ************************************************* ********************************************** **************** ************************* *********************** **************************************************************************************************************************************************************************************************** COST PER DIGESTER MODIFICATION 1 Concrete yd 350 $700 $245,000 $74,000 $319,000 $57,000 $376,000 $1,504,000 Means 2 Mixing equip ea 4 $80,000 $320,000 $96,000 $416,000 $75,000 $491,000 $1,964,000 Vendor Quote 3 New pumps ea 3 $20,000 $60,000 $18,000 $78,000 $14,000 $92,000 $368,000 Derived from previous projects New heat loop - includes heat 4 exchanger, pump, valves, etc. ea 1 $150,000 $150,000 $45,000 $195,000 $35,000 $230,000 $920,000 Derived from previous projects 5 Piping modifications - gas, process ls 1 $100,000 $100,000 $30,000 $130,000 $23,000 $153,000 $612,000 Derived from previous projects 6 Electrical, Controls ls 1 $150,000 $150,000 $45,000 $195,000 $35,000 $230,000 $920,000 Derived from previous projects 7 Building/HVAC modifications ls 1 $150,000 $150,000 $45,000 $195,000 $35,000 $230,000 $920,000 Derived from previous projects

************************************************* ********************************************** **************** ************************* *********************** **************************************************************************************************************************************************************************************************** SUBTOTALS $1,175,000 $353,000 $1,528,000 $274,000 $1,802,000 $7,208,000

P:\Data\GEN\CSpring\23559 - Clear Spring Ranch SHDF Masterplan\DRAFT Report\Appendix C.xls\Digester Modifications